In August 1943 The A. C. Gilbert Co. developed this lighter in collaboration with Mr. J. P. Roysdon of the Engineer Board.  The M2 Fuse Lighter was more weatherproof than the earlier M1 Lighter and basically replaced it in use by the end of the war.  It was waterproof, could ignite fuse underwater and would also ignite fuse at night without showing a flash.  The A. C. Gilbert Co. produced the first contract of 5000 in 1943 and eventually received contracts for over 6 million of the devices.

 The lighter consists of a zinc alloy body, steel striker and striker spring, safety pin, and special base coupler.  The body is a tube turned over on one end and internally threaded at the other.  The striker is a simple shaft with a striker head on the bottom and a hole through the top end.  The striker is forced up against the spring until the end protrudes out the top end and the safety pin can be inserted.  The special base coupler has a spring snout to hold the fuse but it is covered by a shroud for its entire length.  The shroud helps in weatherproofing it and preventing flash if used at night. 

 The lighter is issued complete and ready to use right out of the box.  For use, simply insert the end of the fuse in the coupler and push fully home.  The spring snout will grip the fuse and prevent its removal.  When ready, simply pull out the safety pin which will release the striker to fly down, propelled by the striker spring to hit the primer in the base coupler.  The primer flash will ignite the fuse.

 The lighters were packed in cardboard cartons with a label on the top that stated “ NOTE: TO BE USED ONLY FOR FRONT LINE DEMOLITIONS OR UNDER ADVERSE WEATHER CONDITIONS”.  When packed there is a cardboard tube covering the base coupler and a rubber plug in the end of the base coupler.  The lighters are painted olive green or black with markings in yellow or white.

The A. C. Gilbert Co. in collaboration with the Engineer Board, redesigned the firing device so that it could be made from zinc die cast alloy.  This change simplified production, saved critical brass, include a positive safety and reduced the weight of the device.  It was adopted in mid-1943 to replace the old style. 

The firing device consists of three main parts, the head, body tube and base coupler. 

The head is made to fit inside the main body.  It consists of the body, release pin, loading spring and safety pin.  The body fits into the main body tube and is crimped in so it cannot be removed.   The release pin fits through the bottom up through the top of the body.  The loading spring fits over the release pin and is retained by a washer fixed near the bottom.  Once the release pin is pushed up, the safety pin fits through holes in the body and pin to hold it in place.  A split ring is attached to the end of the release pin to allow a wire to be attached.

The body tube is threaded internally at the bottom and is cast with the constricting well as an integral part.  It contains the firing pin and firing pin spring.  The firing pin is a single piece turned down to form a striker head and shaft with a ridge on the top end.  The top end is split to accept the release pin.  The striker and spring are pushed up with the split end passing up through the constricting well to engage the release pin.  The release pin pushes the striker end apart so that it cannot pass through the constricting well.

The main body tube is cast with a lug on the side.  The lug has a hole through it to attach a short piece of cord to act as an anchor.  The cord is used to anchor the device in place.

The base coupler contains the primer and screws into the bottom of the body tube.

When the device is set, a pull of 3-5 pounds on the wire will pull the release pin up against the pressure of the loading spring.   As the pin is pulled up it pulls out of the split end of the striker.  When the release pin pulls out of the striker the end is free to close and under pressure of the striker spring is forced down out of the constricting well and down onto the primer in the base coupler.  The primer will fire into the detonator attached to it causing it to fire.

The firing mechanism is painted olive drab.  The devices made in WWII are darker than those manufactured post war and are not marked or are marked in yellow.   Post war devices have a lighter green wash and have markings in yellow. 

In February of 1943 Mr. Roysdon of the Engineer Board asked the A. C. Gilbert Company to design a pull firing device that would also fire on release of tension on the trip wire.  The company designed the T3 Pull Release firing device, later standardized as the “Firing Device, Pull/Release, M3”. The first order for 1000 devices was then issued to the company on 3 August 1943.

 The device consists of several parts, the body, ratchet mechanism, striker and striker spring and retaining rod.  The body is cast of zinc alloy in a cylindrical form and has a lug on the side for the anchor cord.  At the top of the body a reduced diameter head is crimped in that has an elongated safety pin hole in it.  The bottom of the body is internally threaded to accept the base coupler.  Internally the body has a constriction about ¼ the way down from the top.  The ratchet mechanism is loosely attached to the retaining rod.  The retaining rod has a head formed at the bottom end and is long enough to fit slightly through the constriction in the body.  The striker is made with a striker head at the bottom, a shaft and slightly wider head at the upper end.   The striker is split to form four jaws at the top end.  The safety pin is made with a reduced diameter in the centre. 

 The body of the device is either painted olive green or has a green wash applied.  The ratchet assembly is  black.  Markings are in yellow giving the designation of the device.

 When assembled, the striker and striker spring are forced up from the bottom of the body until the top of the striker fits through the constriction and engages the head on the retaining rod.  The safety pin is placed through the elongated hole and retaining rod which keeps the striker from passing fully through the constriction under pressure of the spring.  With the top of the striker held at the constriction, the jaws cannot open enough to release the head on the retaining rod.  A positive safety pin is then placed through holes in the side of the body below the striker head.

 When laid, the device is fixed in position with the anchor cord and a trip wire attached to the ratchet mechanism.  The wire is then tensioned until the safety pin is about in the middle of the elongated hole.  The safety pin can then be removed and the positive safety pin removed last.  The wire is taut and when a pressure of 6-10 pounds is applied to the wire it will pull the retaining rod and striker up through the constriction until the jaws on the striker can open enough to release the retaining rod.  The striker is then free to move down under pressure from the spring to strike the percussion cap in the base coupler.  Alternatively, if the wire is cut or removed the striker spring will apply pressure to move the striker and retaining rod down through the constriction until the jaws can open and release the striker to move down under pressure of the spring to hit the percussion cap in the base coupler.

In February 1942 1^st Lt. W. L. Erhardt of the Engineer Board, Fort Belvoir, VA gave the task of producing the pressure switch to the A. C. Gilbert Co.  The firing device was a copy of the British Pressure switch (No. 2 Pressure, Mk. I) with the exception of using an American style base coupler.  The British switch had been introduced in 1941 and was well proven.  Several improvements were suggested by the company including using a keyhole type trigger rather than the hardened shear pin.  This also had the effect of allowing the firing device to be reused in training.  The company produced some 670,000 of this model.

The device consists of a body, pressure head, base plate, and base coupler.  The main portions are made of brass with the base plate made of steel.  The base plate is 1.5 inches wide and 2.5 inches long with two anchor holes in opposite corners.  The body is mounted on the base plate by two flat head bolts through the bottom into the wide end of the body.  The body is brass with a wider end that contains the firing mechanism and a thinner barrel portion that contains the striker and spring and is threaded to accept the base coupler.   A smaller diameter hole is blind drilled into the head to accept the striker shaft.  A larger hole is drilled through the top of head to accept the pressure head.  The pressure head is made of brass and has the bottom thinned down to a trigger pin with a keyhole in it.

When assembled, the striker and spring are placed into the body barrel, the pressure head and spring are placed into the hole in the head and pressed down so the large portion of the keyhole lines up with the small hole in the head.  The striker is forced against the pressure of the spring into the small hole and through the hole in the pressure head.  When pressure is released on the head, the spring forces the head up engaging the small end of the keyhole with the groove in the striker preventing the striker from moving.  A safety clip is engaged between the head of the pressure head (over the spring) and the body preventing the head from moving down.  

When laid and the safety clip is removed, a pressure of 20 pounds or more will cause the pressure head to move down bringing the large end of the keyhole in line with the striker shaft disengaging it from the striker groove.  This allows the striker spring to reassert itself and push the striker forward until it strikes the percussion cap in the base coupler.   The cap fires and initiates the detonator attached to the base coupler and in turn the main charge.

The A. C. Gilbert Co. in collaboration with the Engineer Board, redesigned the firing device in August 1942 so that it could be made from die cast zinc alloy.  This change simplified production, saved critical brass, include a positive safety and reduced the weight of the device.  It was adopted in mid-1943 to replace the old style.  The first contract for this version was for 685,000 firing devices.

The device consists of a body, pressure head and base coupler.  The body is die cast zinc alloy made in a single piece.  It has a basically tubular body with a flattened base for about half the length.  Protruding out from the base are three lugs that are used to fasten the device in place.  A hole in the top of the body fits the pressure head.  The striker which has a firing pin head at one end and a groove in the shaft at the other fits with the striker spring inside the body.  The pressure head has a flat top with a shaft on the bottom.  There is a keyhole in the lower portion of the shaft.  The base coupler is the standard M1 base coupler.

When assembled, the striker and spring are put into the body and forced into the body so that the shaft of the striker fits into a small hole in the back that connects with the hole in the top of the body.  The pressure head with spring are pushed down so the shaft of the striker fits through the large upper hole in the keyhole.  Once the shaft of the striker is pushed through the pressure head is released so that the small portion of the keyhole engages in the groove in the striker shaft.  This holds the striker back in the cocked position.  A safety clip fits over the spring on the pressure head preventing its downward movement.  A positive safety pin is fitted through holes in the side of the body in front of the striker.

The device is supplied with an extension rod.  The rod consists of a length of threaded rod mounted on a cup and an internally threaded tube.  The cup press fits onto the pressure head.  The extension provides between 1.25 and 2.25 inches of extension.

In 1943 The A. C. Gilbert Co. modified the M1 pressure Firing Device to add a three pronged adapter to the pressure head.  The three pronged head was copied from a German mine igniter and allowed better camouflage for the device.  The modifications were minor and were done quickly.

The device consists of a body, pressure head and base coupler.  The body is die cast zinc alloy made in a single piece.  It has a basically tubular body with a flattened base for about half the length.  Protruding out from the base are three tabs that are used to fasten the device in place.  A hole in the top of the body fits the pressure head.  The striker which has a firing pin head at one end and a groove in the shaft at the other fits with the striker spring inside the body.  The pressure head has a flat top with a shaft on the bottom and a threaded hole in the top.  There is a keyhole in the lower portion of the shaft.  The base coupler is the standard M1 base coupler. 

When assembled, the striker and spring are put into the body and forced into the body so that the shaft of the striker fits into a small hole in the back that connects with the hole in the top of the body.  The pressure head with spring are pushed down so the shaft of the striker fits through the large upper hole in the keyhole.  Once the shaft of the striker is pushed through the pressure head is released so that the small portion of the keyhole engages in the groove in the striker shaft.  This holds the striker back in the cocked position.  A safety clip fits over the spring on the pressure head preventing its downward movement.  A positive safety pin is fitted through holes in the side of the body in front of the striker.

The device is supplied with an extension rod and three pronged adapter.  The rod consists of a length of threaded rod and an internally threaded tube.  The three pronged adapter has a base with three wire prongs attached by a bolt to the top.  The adapter can be screwed directly onto the pressure head or can be attached to the extension rod which is then screwed onto the pressure head.

When laid and the safety pin and clip are removed, a pressure of 20 pounds or more will cause the pressure head to move down bringing the large end of the keyhole in line with the striker shaft disengaging it from the striker groove.  This allows the striker spring to reassert itself and push the striker forward until it strikes the percussion cap in the base coupler.   The cap fires and initiates the detonator attached to the base coupler and in turn the main charge.

This firing device was introduced during WWII.  It is strictly an American design not taken or designed from any devices in service with anyone else.  At first glance, it seems an overly large but it is designed that way to be the same size as the standard US Army ½ and 1 pound demolition blocks.  One of the manufacturers of this device was the Geometric Stamping Co. of Euclid Ohio.

The body of the device is a stamped sheet metal box with rounded edges.  One end is open, the other closed with a stem spot welded on to hold the base coupler.  The other end is closed by a removable stamped sheet metal cap.  The firing pin is inserted in a small hole in the centre of the stem and held on by a press fit washer.  The firing hammer mechanism is riveted inside just above the stem.  On the outside of the device, held on by the same rivets as the firing mechanism, is a bracket for the safety pin and release plate.  The release plate is formed of sheet metal with a tail, plate and a portion formed on the bottom to fit into the bracket.  There are two holes punched in either side of the device opposite each other.  There are small tubes inserted in the holes that leave a space between them.  These holes are used for a positive safety in that a nail or rod inserted through the holes will block the travel of the firing hammer before it can strike the firing pin.

There are mounting brackets spot welded onto the bottom of the body.  The earlier (WWII) firing devices have a mounting bracket ¾ inch wide at 90 degrees from the stem with a single hole on either end.  These are bent up around the device until required.  A later version has the mounting bracket turned 90 degrees and is angled in appearance.  At the back end (over the end cap) is a single hole, at the other end, which is bent up around the stem there are two holes.  Other than the mounting brackets, the devices are identical.

 When the device is assembled, the tail of the release plate fits through a slot in the top of the body.  The tail engages in a slot in the cocked firing hammer.  The release plate is then pushed down into the bracket and the safety pin inserted to hold the device in the cocked position.  The base coupler screws into the stem and pushes the loose firing pin back into the device.

 The devices are unpainted but do have some type of protective coating.  On the older devices “This side up” is printed on the top of the release plate.  On newer devices, it is stamped into the release plate.  No other markings have been noted.

 A weight of at least two pounds is required to hold the release plate down.  When the weight is removed the firing hammer, under pressure of its spring, pulls down on the tail of the release plate.  Once it has travelled far enough, the plate disengages leaving the hammer free to rotate under pressure of the spring until it strikes the firing pin.  It forces the firing pin forward to hit the percussion cap in the base coupler which fires and causes the attached detonator to fire.

In June of 1943, Captain Terbert of the Engineer Board gave the A. C. Gilbert Co. a model of a release device and asked them to incorporate some changes to the model and make samples.  Once the samples were produced and approved a number were made for training.  During training it was found that further changes and improvements were required.  Several revised models were produced until one finally satisfied all the requirements of the Engineer Board.  The final model was standardized as the “Firing Device, Release, M5”

 The device is made of sheet steel and is press formed into an open topped rectangular box.  On the bottom of the box is a hole threaded to accept the base coupler.  The release plate is hinged on the top on the opposite end to the hole in the bottom.  The release plate is bent to form a hinge at one end and near the other end is bent to form a dip for the safety pin.  A piece of spring steel is riveted onto the release plate so that it will put pressure on the safety pin to hold it in place.  A spring loaded striker is hinged in the middle of the box so that when the striker rotates the striker point will strike the percussion cap in the base coupler.  There are holes in the side of the box, one set for the safety pin that line up with the dip in the release plate, the other larger set allow a pin or nail to be inserted to block the travel of the striker.  The safety pin has two grooves turned into it that will slightly engage the sides of the mechanism and make removal more difficult if the release plate is not fully down.  A small cotter pin through one end of the safety pin prevents accidental removal.

A minimum weight of 5 lbs is required to hold the release plate down when laid.  When the weight is removed the striker spring reasserts itself and causes the striker to rotate.  The rotating striker pushes up on the release plate until it is pushed out of the way and the striker is free to completely rotate and hit the percussion cap in the base coupler.  The percussion cap will cause the detonator attached to the base coupler to fire.

In 1942 the A.C. Gilbert Co. was manufacturing the British No. 10 Mk. I delay on behalf of the OSS.  They were asked by Capt. Erhardt of the Engineer board to convert them to American standards that could be used with standard American mines and demolition blocks.  This proved to be a simple task simply modifying the standard base coupler to fit the end of the device.  In effect all that was required was to remove the spring snout used on the British device and replace it with the redesigned base coupler.  The A.C. Gilbert Co. produced 1.8 million on the first contract another 1 million in 1943 and in 1944 were working on a contract for 2.75 million.

 The device is of the chemical delay type.  It consists of a two part cylindrical case, the upper section of copper, and the lower section of brass.  A modified base coupler is permanently attached at the bottom end.  The lower section contains the spring-loaded striker held in the cocked position by a wire running from the striker through the top section to a retaining screw at the top.  Earlier production firing devices have a single inspection hole above the coloured safety strip at the lower end of the bottom section.  In later production there are two inspection holes with the safety strip between them.  In addition in the later production the safety strip has been moved slightly higher on the body.  The top end contains a glass ampoule containing a corrosive liquid (Cupric Chloride) and two pieces of cotton wicking.  The top portion of the device is sealed by plugs and by a lead washer on the retaining screw.

 Before use the device must be examined by looking through the inspection holes to ensure the striker is still held in position.  If not, the device is discarded.  When the device is to be used a detonator is crimped onto the base coupler.  When laid the upper copper portion of the casing is crushed from both sides causing the glass ampoule to break and release the corrosive liquid.  The corrosive liquid acts on the retaining wire eventually weakening it enough to break under the pressure of the striker spring.  When the wire breaks, the striker, under pressure from the striker spring is forced down onto the percussion cap.  The percussion cap fires and sets off the detonator.

 The safety strip is colour coded according to the nominal delay of the device.  When initially developed there were six different delay periods. The nominal delay times for the switches were timed at 70 degrees Fahrenheit.  The delay strips were painted in six different colours giving delays of: black 12 min, red 14 min. White 1 hr 45 min., Green 4 hrs, yellow, 6 hrs 15 min. and blue 17 hrs 30 min.  The delay times are effected by atmospheric temperatures. 

 The firing device is normally unpainted, the top is natural copper coloured, the bottom portion natural brass coloured.  The safety strip is painted to denote the delay times as listed above.

In September 1942 Major Erhardt and Mr. J.P. Roysdon of the Engineer board presented the A.C. Gilbert Co. with the project of developing a friction igniter, similar to a German device.  The device was to be made of plastic and had to be small, waterproof, and as non-metallic as possible.  The company produced many lots with slight revisions before it finally met all the requirements.  This was the “Pull Type Firing Device, T2” which was later standardized as the “Firing Device, Pull, Friction, M2”.  The construction of this device almost eliminated the use of critical war materials.  While the device was developed and test lots made by A.C. Gilbert Co. final production was passed to another company.

During development of the T2, there were two other models produced, the T2A and T2B.  These differed slightly from the T2 and test lots of 500 each were produced in 1944.  Unfortunately no other information is available.

The entire device is constructed of black bakelite and a small amount of steel.  The body is cylindrical and has a non-removable base coupler on the bottom.  The body contains a pellet of friction compound in the top of the base coupler.  A steel wire coated with red phosphorous fits through the top of the body, through the pellet and into the stem of the base coupler.  A safety pin fits through the side of the body and through a twisted portion of the wire.  A coil spring is attached to the looped end of the wire.  The base coupler has a celluloid cup filled with desiccant protecting it.

For use a detonator is crimped onto the base coupler.  A slack trip wire is attached to the spring.  When a load of 3-9 pounds is applied to the trip wire, it will stretch the spring then snap the friction wire out of the device.  That causes the red phosphorous on the wire to pull through the friction compound causing a flame to flash through the base coupler and ignite the detonator.  The device is not totally waterproof and should if possible be used where it is protected from moisture.

There is apparently a zinc alloy bodied version.  Little is known about this version other than it operates in exactly the same manner.  Possibly this is a T2A or T2B.

Development of this igniter started as a British requirement for a method to initiate several Limpet mines at the same time without the need to connect them with primacord.  The SOE (Special Operations Executive) requested help from the OSS (Office of Strategic Services) in the development of a sympathetic fuze.  After the OSS initiated the development, the Army and Navy found they also had use for such a device.  After much research and development, the resulting device became the “M1 Concussion Firing Device”.  It is a mechanical device actuated by the concussion of a nearby explosion.  In use, a single explosion will cause any charges equipped with the firing device within range of the initial explosion and others within range of the other devices to fire.

 The body of the device is mushroom shaped and made of diecast metal.  The base is a cylindrical tube that ends in a large flat head.  The head is threaded to accept a protective cover that has a waffle pattern protective grill on the outer face.  The waffle pattern allows the concussive wave to enter the device but still protects the inner workings from damage while in transit or handling.  The head contains a release spring, phosphor bronze snap diaphragm and rubber cover. The base tube is threaded at the bottom end to accept a base coupler.  The base tube contains the striker and firing pin spring.  The striker has a beveled shoulder about half way down and a groove at the end to engage the release spring.  Just behind the head is a cylindrical pellet sleeve cast onto the base tube.  The pellet sleeve contains a safety ball, spacer, perforated sleeve plug and salt pellet.  The spacer is held in place by a safety pin.  The pellet sleeve is covered by a cardboard cap.

 Inside the head, the diaphragm is in the convex position.  In the safe mode, the striker is held in contact with the diaphragm by the safety ball protruding through the bottom of the pellet sleeve into the base tube with the beveled shoulder of the striker against the ball.  When being emplaced in water either of two salt pellets is inserted in the sleeve plug and put into the pellet sleeve.  A blue pellet will give an arming delay of approximately 3.5 minutes, the yellow pellet a delay of 7 minutes.  When the safety pin is removed and the pellet sleeve cover removed the salt pellet begins to dissolve.  As it dissolves it will allow the safety ball to move upwards under pressure of the beveled shoulder and striker spring.  The striker will move forward about 1/16 inch out of contact with the diaphragm and be held only by the release spring.  The device is now armed.  When the concussive wave from an explosion enters the head, it causes the diaphragm to invert to the concave state hitting the end of the striker and forcing it out of the release spring.  The striker spring then forces the striker down to hit the percussion cap in the base coupler.  When emplacing in air, the salt pellets and plug are discarded.  The device will be fully armed as soon as the safety pin is removed.  The device will function when a pressure of about 9 pounds per square inch is applied to the diaphragm face.

 Underwater the device should not be used under 15 feet of water as the hydrostatic pressure of the water below that depth could cause the device to function.

 The device is painted olive green with markings in yellow.

These were introduced for use where a short delay was desirable.  They could be used in assault demolitions or rigged with a trip wire.  They are waterproof and could be used underwater.  No information has been found to differentiate between the M1 or M1A1.

 They consist of a cylindrical plastic housing that has a friction igniter in the top end.  A pull wire protruded out the top end with the bottom of the wire coated in a friction compound and embedded in a flash compound.  A safety pin fits through the side if the body to hold the wire in position until ready for use.  The top of the wire has a round ring attached.  The bottom end of the device has a combination detonator and delay element permanently attached.  The detonator element is covered by a plastic protector that screws onto the standard threading at the bottom of the top portion.

 The device is made of olive drab plastic and has the delay stamped into the body.  The circular ring attached to the friction wire identifies this as a 15 second delay, especially useful in low light situations.

 For use, the protective cap is removed and the device screwed into a standard demolition charge.  When ready for use, the safety pin is removed and the pull ring pulled out with a sharp pull.  This action draws the friction wire through the flash compound causing it to ignite.   The resulting flash ignites the delay element which burns down and fires the detonator.

This is a US Navy device modified from the earlier Mk. 1 Mod 0 device.  Depending on how it is set it can operate as a pressure, pull or release device.

 The device consists of a body, trigger pin, firing pin, base, bail and knurled nut.  The body cast as a single piece incorporating the main body, barrel and base.  The body has two holes drilled through it.  One hole is from the top, the other through the end.  The end of the barrel is internally threaded to accept a standard base coupler.  The bail is attached centrally on the main body.  There are four mounting holes in the base.  The trigger pin has two slots connected by a central hole and a threaded hole in the bottom.  The top of the trigger pin has a flat trigger button screwed on the top.  The firing pin has a striker head at one end and is threaded on the opposite end.  A circumferential groove in the middle of the firing pin shaft fits the slots in the trigger pin.  The knurled nut fits on the threaded end of the firing pin.  There is a positive safety pin that fits through holes in the side of the barrel blocking travel of the striker.

 There are two attachments supplied with each device.  The ratchet reel replaces the trigger eye so that a more accurate adjustment of the trip or tension wire can be made.  In addition there is a three pronged trigger button that can replace the flat button.

 When assembled, the trigger pin fits through the top hole in the main body with a trigger spring fitted over it.  The firing pin and firing pin spring then fit through the barrel with the shaft passing through the trigger pin and is held in position by the knurled nut.

 For use as a pressure device the trigger pin is in the “Up” position with the groove in the striker fitting into the bottom slot in the trigger pin.  When the knurled nut is removed and pressure applied on the trigger button, it will push down against pressure of the trigger spring and bring the centre hole in the trigger pin in line with the striker shaft allowing the striker under pressure of the striker spring to move forward to hit the cap in the base coupler.

 For use as a release device the trigger pin is in the “Down” position with the groove in the striker fitting into the upper slot in the trigger pin.  A weight of at least 11 pounds is required to hold the trigger pin down against the pressure of the trigger spring.  When the knurled nut is removed and pressure removed from the trigger button, it will push up by the pressure of the trigger spring and bring the centre hole in the trigger pin in line with the striker shaft allowing the striker under pressure of the striker spring to move forward to hit the cap in the base coupler.

 For use as a pull device it is anchored at one end by the bail and the ratchet reel screwed into the bottom of the device.  The trip wire is attached to the ratchet reel.  The trigger pin is in the “up” position with the groove in the striker fitting into the bottom slot in the trigger pin.  When the knurled nut is removed and pressure applied to the trip wire it will pull against pressure of the trigger spring and bring the centre hole in the trigger pin in line with the striker shaft allowing the striker under pressure of the striker spring to move forward to hit the cap in the base coupler.  It can also be used as a tension release device by applying enough pressure on the trip wire to pull the trigger pin through into the “Down” position.  When the tension on the wire is released the trigger spring will apply pressure to the trigger pin pulling it up until the striker shaft lines up with the central hole and the striker is released to hit the percussion cap.

In 1943 the OSS arranged for the production of AC delays in the US as the British were having problems producing enough.  The American version is an exact copy with minor cosmetic differences.  The AC delay was used throughout the remainder of WWII and was later adopted and produced by the CIA.  It was also used by the Army and Navy.  The AC delay saw considerable use in Viet Nam.

They are comprised of a round brass body made with a two stepped threaded end, the smaller set of threads for the burster and the larger set to screw into the limpet or charge container.  It could also be fitted with a fuse cap instead of the burster.  The opposite end is threaded to fit an end cap that is drilled and threaded to accept a thumb screw.  The most obvious difference between the British and American production is the thumb screw.  The grip on the British version is rectangular, the American is oval.  A safety pin with cord attached fits through the end cap and thumb screw preventing it from being screwed in.  Contained within the body is a spring loaded striker that is held in the loaded position by a celluloid disc attached to a tapered tail on the striker.  Lint is packed in a brass sleeve screwed into the body just above the striker holding the striker and disc in place.  American celluloid is different than British celluloid and did not work properly.  Until a suitable substitute was found the OSS obtained British celluloid which was used until the end of WWII.  By then a suitable substitute had been found and was used for post war production.  All threaded joints are fitted with rubber washers to waterproof the device to a depth of 70 feet.

 For use, the device is loaded with an ampoule containing acetone to give the desired delay time.  The ampoule is loaded by removing the end cap, inserting the ampoule and replacing the end cap.  When ready to initiate the device, remove the safety pin and screw the thumb screw in until the ampoule breaks.  The acetone soaks into the lint and begins to work on the cellulose disc softening it.  When the disc is softened enough, the striker under load of its spring will pull through the disc and fly forward to hit the cap in the burster.

 The device is normally painted grey with no other markings.  The thumb screw has a diamond shaped area engraved that appears to provide a firm gripping surface.

 The OSS AC Delay is issued in a sheet metal box containing the device, six ampoules, a burster in a wooden container, wrench and an instruction sheet giving the nominal delay times.  Depending on the temperature, the delays differ, at lower temperatures the delay times are increased, at higher temperatures the delays are shortened.  As an example, at 60 degrees F the nominal delay times are: Red- 4.5 hours, Orange- 7.5 hours, Yellow- 15 hours, Green- 26 hours, Blue- 42 hours and Violet- 5.5 days.  In 1944 the OSS requested asked for the development of AC delays with a delay time of up to 30 days.  This was done and three more ampoules made available giving delay times to 30 days.  Also, in 1944 for training,  an AC delay was developed using two other ampoules giving delays of five minutes and 30 minutes in conjunction with a perforated disc replacing the celluloid disc.  These were not issued for field use.

The CIA continued with production of the AC Delay post WWII.  The CIA produced a Mk. II version in the 1950’s and a Mk. III version in the 1960’s.  Exactly what the differences between the three versions are is unknown at this time.

 One difference that can be noted from the OSS produced version to the CIA produced version is in the threaded cap housing the thumb screw.  It appears that the WWII version has the cap knurled to provide a gripping surface, in the post WWII versions the cap is ribbed.

 The CIA produced kits that contained up to 10 ampoules, Red 3 hours, Orange 7 hours, Yellow 15 hours, Green 20 hours, Violet 100 hours, Black 30 days, Clear 50 days, Gold 60 days, white unknown, grey unknown.  These delay times are those given for a temperature of 77 degrees F.  Delay times are increased for colder temperatures and reduced for warmer temperatures.

The CIA also introduced an incendiary head to replace the burster.  The incendiary head would ignite immediately upon being struck by the striker and would burn very brightly with an intense heat for 4 to 6 minutes diminishing after that to being completely expended in 10 minutes.

The M142 was introduced into American service in about 1972.

 The device is a compact unit capable of initiating a boobytrap via Pull, Pressure, Release, or Tension Release depending on how it is set.  The device will operate under a pressure of 11.3 kg, a pull of 3.2 kg, or a release of pressure or tension of 1.1 kg.

 The device is made of plastic in a basically cylindrical form.  There are lugs and recesses molded onto the body that allows it to be screwed, nailed or wired in almost any position.  A slot in the top of the body accepts the sear plate that is held in position by two pins, one with a round head, one with a square head.  A positive safety pin fits through the barrel of the body preventing the striker from hitting the percussion cap.  An alternative set of holes for the positive safety are located at 90 degrees from the normal holes.  The striker is made of aluminum with a plastic four pronged guide and spring stop near the point.  The rear portion of the striker has a groove that engages the sear.  A striker spring fits over the striker.  The striker and spring fit into the body compressing the spring until the sear on the bottom of the sear plate engages the groove in the striker.

The device is issued in a round plastic case containing everything required to set the device in any mode.  Contained within the case is the device, roll of steel trip wire containing 15 metres of wire, a strip of tape containing screws and nails, a tension release attachment, base coupler and an instruction sheet.  The coupling base is also issued separately.  Early issues of the device were packed in round tin boxes.

 The firing device is normally used with the Coupling base but the US M1 Base coupler can also be used.

The device is made of olive green plastic, as are the base couplers.  The base couplers have a yellow or brown band around the centre.

 The mode of use determines which pins are taken out to set the device.  For use as a release device, the round headed pin is removed.  For use as a pressure device, the square headed pin is removed, for use as a pull device, the square headed pin is removed, and for use as tension release it must be fitted with the attachment and have the round headed pin removed.  It should be noted that the two pins are not interchangeable as they are made from different gauges of wire with corresponding holes.

The M147 is not used in general demolitions.  It was primarily designed to provide Special Forces with a device that could accurately initiate a timed demolition.  It is very reliable, not effected by temperature to any great degree, has accurate timing and can be used underwater.  It is also hardened against outside sources of electro-magnetic interference to prevent premature firing from those sources. The device covers all time ranges from 5 minutes to 30 days. 

 The body of the M147 is made of welded aluminum in a rectangular shape.  The top of the body has a coupling nut permanently attached to allow an M7 nonelectric detonator to be attached.  The detonator is not crimped onto the coupling but is held in place by a plastic coupling nut to ensure a waterproof seal.  The side of the body has a safe/arming indicator in the top left corner and at the bottom the time display window.  The bottom of the body has two buttons used to set the time delay.  On the right side of the body is an arming tab, rotor, locking button and indicator mark.  The arming tab is used to move the rotor.  The rotor is marked with three letters, A (Armed), S (Safe), T (Timing).

 The body contains a reserve cell battery.  The battery has an extremely long life as the electrolyte is kept separate from the electrodes until the first step of the arming procedure is performed.  The body also contains the clock unit, M100 electric primer, piston actuator and a safety interrupter.

 For use the device is prepared by:

- lifting the arming tab 180 degrees from the body.  The “S” on the rotor should be beside the indicator mark.

-Rotate the rotor 90 degrees until the “T” is beside the indictor mark.  This activates the battery.  The LCD display should read all 8’s, diamond symbols and underscores. 

-The time is set by pushing the left button once so the display goes blank, press it once more and the display will read all zeros with a 5 on the right.  An underscore(cursor) will be under the left hand zero.  Each time the left button is pushed the cursor moves one position to the right.  There are three sets of two digits representing days/hours/minutes reading from the left.  To set the time position the cursor under the digit desired and hold the left button down, press the right button to change the digit.  Each press on the right button moves an increment of one.  Release and press the left button to move to the next digit.  Continue until the desired time is set. 

-Take the arming tab in one hand and with the other press down the locking button, rotate the rotor until the “A” is aligned with the indicator mark.  Check the display to ensure the minutes and seconds of the 5-minute arming delay is showing.

 -Turn the rotor back to the “T” position, the arming delay will stop and the display should now show the delay time. 

-Install the M7 detonator using the coupling nut. 

-Arm the device by turning the rotor to the “A” position.  This starts the 5-minute delay again and the display should show the countdown of the delay. 

-Lower the arming tab and connect the device to the charge.

  Once the 5-minute delay has elapsed the display will show a pair of flashing diamonds.  The internal piston actuator functions removing the safety interrupter and putting the primer in direct line with the detonator.  The safe/arming indicator changes from a green “S” to a red “A”.  The device is armed and functioning.  Once functioned this device cannot be stopped or reset.  When the delay time expires the M147 applies power to the primer that then fires the detonator and explosive charge.

 The M147 is painted olive green.