The Mk. II Grenade

BACK

When the Mk. I grenade was condemned by the AEF in May of 1918 the Americans were again without a defensive grenade of their own.  With an offensive planned for the spring of 1919 it was imperative that a new grenade be designed and produced without delay.  American industry proved to be up to the task and by August 1, 1918 had the new grenade designed and much of the required machinery produced and installed.  Initial orders called for 44 million grenades.  A daily production figure between 250,000 and 300,000 was achieved by November 11, 1918.  Over 21 million were produced by December 6, 1918.  According to records only 516,533 had been shipped overseas.  Companies involved in producing grenades or parts were: Spacke Machine & Tool Co., Stewart-Warner Speedometer Co., American Radiator Co., International Harvester Co., Miami Cycle & Manufacturing Co., Doehler Die Castings and Precision Casting Co.

The new grenade was favorably accepted by the AEF and became the standard American fragmentation grenade.  This grenade was used for a number of years after the war and was likely supplied to allied countries such as the Philippines.  An account of an action on Corregidor just before its surrender noted “With nothing more powerful than rifles, a few light machine guns, and moldy 1918-vintage hand grenades, the defenders had not a single weapon capable of slowing down much less stopping a tank”. 

The Mk. II grenade has gone through many modifications since 1918.  It is difficult to pin down exactly when particular modifications were made.  There have been changes to the body, filling changes, many fuze changes and colour changes in its career with many of the changes overlapping. 

The bodies are quite varied, depending on manufacturer, but there seems to be four main types of body.  The first body which is not included in the four, was that of the Mk. I grenade.  Period manuals seem to indicate that when the fuze mechanism was modified to the Mk. II style, some use at least was made of the surplus Mk. I bodies with the new fuze mechanism.  That use may only have been as practice grenades.

The first truly Mk. II body was designed in 1918.  Made of cast iron it is about 2.25 inches diameter and 3.5 inches high.  The lower portion of the body is divided into 40 segments (8 vertical rows of 5).  The bottom is drilled and tapped to form a 3/8” filling hole closed by an aluminum alloy filling plug.  The body tapers toward the filling hole leaving only a thin rim between the outside of the body and hole.  The upper cone is divided along the same vertical lines as the body.  The transition shoulder from the cone to main body is quite rounded.  The body at the top of the cone is threaded to accept the fuze mechanism.  The body may be marked with the manufacturers mark on one of the segments and may have a mold number on it.

 The second type body was produced in the 1920’s.  The basic shape is the same but is slightly shorter.  The base was widened around the filling hole and the transition between the top cone and main body became much squarer.  The grooves in the body still divide the body into 40 segments.  The upper cone is divided vertically but the grooves do not attach to the vertical grooves of the body.  The body may be marked with the manufacturers marking on one or more segments and may have mold numbers on other segments.

 The third type body seems to be a minor modification that appeared sometime in the 1930’s.  It is of basically the same configuration as the second body but the vertical grooves in the upper cone are continuations of the vertical body grooves.  This version is most likely a simplification of the body to ease manufacture.

 The fourth body is the same as the third but eliminates the lower filling hole and has a solid base.

 There are many variations on all the body styles due to the different manufacturers.  The segments may be more or less defined, the grooves can be slightly wider or deeper, the top surface of the segments can be flatter than others.  Even with the many variations the bodies should all fit within the basics listed above.

 

Defensive Grenade, Mk. II

Igniter- Bouchon and Detonator Assembly Mk. II

 Period photos suggest that Mk. I bodies with the new fuze mechanisms were initially used.  The body however had also been redesigned, while maintaining the basic “lemon” shape the upper cone was higher and thinner and the projection on the bottom eliminated.  The bottom has a 3/8” threaded hole used for loading the charge.  An aluminum alloy plug coated with asphaltum was used to close the filling hole.  The external segmentation was deeper than on the Mk. I body and had 8 vertical lines of 5 segments.

 The new fuze mechanism “Bouchon and Detonator Assembly Mk. II” functions similarly to the Mk. I.  The fuze cover and safety lever are formed as one piece rather than the two distinct pieces of the early mechanism.  The “Tail” was eliminated and the bottom of the mechanism closed by a fuze sealer to prevent the entrance of dirt or mud into the mechanism.  Initially Mk. 1 Bouchons were modified by cutting off the tail to allow the new lever to fit.

 The filling was normally 1.85 oz. of  TNT.  A shortage of raw materials caused a shortage of TNT and thus a rationing of it.  Because of the rationing the grenade could also be filled with Amatol 50/50, a mixture of 50% ammonium nitrate and 50% TNT.  As the rationing continued a filling developed by the Trojan Powder Company of Allentown PA and subsequently called “Trojan Powder” was used.  On 19 October 1923 grenades loaded with Trojan Powder were declared unserviceable (OCM 3332).

 The grenade body is painted grey.  The grenade was still in use in 1926 when the specification for color was changed to yellow.  Examples have been found that have been repainted to the new specification.  There is however a notation in TR 1350B dated May 16, 1930 that grey painted grenades would still be found in service.

   

Fragmentation Hand Grenade H.E. Mk. II

Igniter- M5

After July 1925 the grenade was redesignated as “Grenade Hand, Fragmentation, HE Mk. II” to conform to new nomenclature standards.  This grenade uses the first or second body type and is fitted with “Detonating Hand Grenade Fuze M5”.  The body is filled with 1.85 oz. of loose granular TNT.  This grenade was used through the 1920’s to the early 1940’s.

The grenade body is painted yellow.  The fuze mechanism is unpainted.

The filled grenade bodies were issued separately from the fuze mechanisms.  24 grenades were packed in a box with the grenades separated by spacers.  The grenades were shipped with a wooden plug screwed into fuze hole.  The wooden plug extends into the body and when withdrawn leaves a cavity in the explosive for the detonator.  The fuze mechanisms were packed 384 to a wooden crate.  A spanner wrench was included with each box of fuzes to be used to firmly seat the fuze into the grenade.  Grenades were fuzed just prior to use.

  

     

 

Grenade, Hand, Fragmentation, Mk.II

Igniter- M10, M10A1, or M10A2

This grenade used body type 2 and later body type 3.  The grenade with a filling of EC blank fire powder was adopted as standard on Oct 21, 1926.  It was initially fitted with the M10 igniting fuze with a short lever.  In 1930 the lever was extended to 4 inches to make the grenades safer to handle.  In early 1942 the igniter mechanism was changed to the M10A1 and in late 1942 to the M10A2.  The body was filled with 0.74 oz of EC Blank fire powder.  Declared limited standard in 1943.

 The body of the grenade was painted yellow from 1926 to 1942.   In October 1942 the Ordnance committee recommended that ammunition filled with HE, including grenades, should be painted in a lusterless olive drab paint with infra red reflecting pigments.  All newly manufactured grenades were painted in the new colours.  Grenades in depots were repainted green and those in the hands of troops would be repainted if practicable.  A yellow band around the top of the grenades denoted a filling of HE.

 The grenades were issued fuzed.  Prior to 1941 the Mk. II grenades were packed in boxes containing 25 grenades separated from each other by spacers.  In a contract (W-672-ORD-3446) issued in April of 1941 to the Antonelli Fireworks Co. Ltd the Mk. II grenades complete with fuzes were refitted with the M41 fiber container.  Tests concluded that grenades packed in individual containers within a box were not liable to mass detonation should one explode.

 

 

 

Grenade, Hand, Fragmentation, Mk. IIA1

 Igniter- M10A3

 In 1943 this designation was adopted to differentiate this model with the M10A3 fuze from the grenades with earlier fuzes.  Declared limited standard  on 6 April 1944 with the adoption of the Grenade, Hand, Fragmentation, TNT, Mk. II.

 The Mk.IIA1 could be found with either the earlier body with a filling hole or the newer body without filling hole.  It was up to the manufacturer which body style was used.  The grenade is fitted only with the M10A3 fuze mechanism.  The filling is 0.74 ounces of EC Blank fire powder.

 The grenade is painted olive green with a yellow band around the top of the body.  The fuze mechanisms are not painted but the levers may be coloured green.  Markings on the top of the lever give the designation of the fuze mechanism. 

 The grenades were shipped fuzed in boxes containing 25 grenades.  Each grenade is separately contained within an M41 container.

 

Grenade, Hand, Fragmentation, TNT, Mk. II

Igniter- M6A4C, M204, M204A1, M204A2

Testing of the grenades in use concluded that fragmentation grenades loaded with TNT produced more fragments that were projected at higher velocities to greater distances than grenades loaded with EC Blank fire powder.  As a result, new grenades were to be loaded with 2 ounces of TNT.  These grenades normally used the fourth body type without filling hole.  They were fitted with the Fuze, Detonating Hand Grenade M6A4C.  The grenades were later fitted with the M204 series of fuze mechanism. This grenade became standard in April 1944 and continued in use until replaced by the M26.  Large quantities remained on hand and were used throughout Korea and into the conflict in Vietnam. 

The grenades were painted Olive green with a yellow band around the top of the body.  The fuze mechanism is marked on the top of the lever with the designation and lot number.

The grenades were packed in boxes containing 25 grenades complete with fuzes.  Each grenade is individually packed in the M41 fiber container which prevented sympathetic detonation.

   

Mk. II Practice Grenades

 

During the First World War when the Mk. II was first developed, in addition to the 17 million defensive grenades produced to Nov. 8 1918, they also produced 3.6 million practice grenades and 415 thousand dummy grenades.  “Americas Munitions” does not indicate whether the practice grenades were Mk. II or Mk. I grenades.  The Manual for Hand Bombers of July 1918 mentions practice grenades under the Mk. I section, but no mention is made in the section on the Mk. II.  The manual describes the practice grenades as being similar in every way to the live grenade but omitting the explosive charge, detonator, fuze and filling hole plug.  This indicates that the practice grenades of the first war and immediately after were more of an instructional type grenade rather than the practice grenade as it later became.  It is likely that Mk. I bodies were utilized with the fuze mechanisms changed to the Mk. II type to stay current with the live grenades in service.  It is also likely that some Mk. II bodies were also utilized.  In the standards of the time, these grenades were painted red. 

 In 1923 a form of practice grenade was developed and sent for testing.  The grenades used the standard body and Mk. II fuze mechanism with No. 6 detonator.  They also had a filling of sand and powdered Soapstone and were plugged with a cork.  When the grenade detonated it was supposed to blow out the cork and provide a visible signature from the expelled soapstone powder.  The actual results of the testing are unknown but subsequent types of practice grenades would indicate that it was found that the filling of sand and soapstone was unnecessary. This seems to be the birth of the practice grenade as it is now known.  This all suggests that the Mk. II practice grenade came into being in about 1924 or 1925.

 The Mk. II practice grenades were simply the standard grenade body without filling hole plug and using a normal fuze mechanism as a practice charge.  The filling hole in the bottom was closed by a cork. 

 

Grenade, Hand, Practice, Empty, Mk. II

Igniter- Mk II, M5

 

The first version introduced into use utilized the standard body and the Mk. II Bouchon assembly with No. 6 detonator.  The filling hole was closed by a cork.  Believed to have been first introduced in the 1924-25 period.  The body was painted red at this point.  When the colour changes were made in 1926 it is likely the colour of the practice grenades was also changed from red to blue.   The use of the Bouchon Assembly Mk. II with No. 6 Detonator continued in use until at least 1936.  At that time it was obsolete for future manufacture having been replaced by the M5 and later the M10 fuze mechanisms but as stocks remained it was to be used for practice until exhausted.  The No. 6 detonator provided a loud report with a bit of smoke.  Sometime between 1930 and 1936 this version was declared limited standard.

 

     

Grenade, Hand, Practice, Mk. II

Igniter- M10, M10A1, or M10A2

This version used a standard body with the “Hand Grenade Igniting Fuze M10”.  Due to the use of an igniting fuze rather than one with a detonator a practice charge is required to provide a loud report and small puff of smoke.  The practice charge contains 22 grains of black powder pressed into pellet form.  The practice charge is contained in the lower end of a paper tube 1/16 inch in diameter and 1.25 inches long.  The bottom of the tube is closed with a chipboard disc with a similar disc inside the tube on top of the charge. 

 When the grenade is loaded the fuze is assembled to the body and the practice charge inserted through the filling hole.  The charge fits over the lower end of the fuze and the filling hole closed by a cork.  The cork holds the practice charge in place until the grenade is fired.

When the grenade is fired, the practice charge blows the cork out, produces a loud report and a puff of white smoke.

 This was the standard practice grenade until it was declared limited standard in 1941.

 In February 1941 the Ordnance Committee recommended that the Practice grenade be declared limited standard in favor of the Grenade, Hand, Dummy, Mk. 1.  It was felt that the requirements of training did not need a grenade with an explosive charge that cost almost as much as a live grenade but could be fulfilled by the dummy grenade costing much less.  Despite it being declared limited standard it never fell out of use and in 1942 when the M10A1 fuze was adopted they were also used with the practice grenade.  They were later fitted with the M10A2 fuze mechanism as they came into use and older fuze stocks were used up.

 By 1944 the practice grenade was returned to a standard piece of equipment.  The practice grenades not only gave practice in the operation of a grenade and throwing accurately but also accustomed the troops to the delay action of the fuze, something a dummy grenade could not do.

 Due to the longevity of the grenade bodies, the practice grenades could be found with any of the fragmentation grenade body types except those which did not have a filling hole.  Samples survive indicating that Mk. I bodies may also have been used as practice grenades during WWII.

 

     

Grenade, Hand, Practice, Mk 2A1

 Igniter- M10A3

 

This is a little known version of the practice grenade.  Not listed in any of the manuals it can only be assumed that its service life was extremely short.  It is noted as using the M10A3 igniting fuze.  It is likely that this grenade was redesignated as the M21 grenade to prevent confusion in supply.

 It is listed in the “Standard Nomenclature List No. S-4” dated 1 November 1944 and later as an obsolete item in “Department of the Army Supply Catalogue ORD 5 SNL S-10” dated July 1950.

Grenade, Hand, Practice, M21

Igniter- M10A2, M10A3, M205, M205A1, M205A2


It appears that the M21 grenade was designated in 1943/44.  Most likely it was simply a redesignation of the Mk. 2 and Mk. 2A1 practice grenades to prevent errors in supply.  Having grenades designated similarly could cause problems when ordered from supply.  ``Grenade, Hand, Fragmentation Mk. 2`` and ``Grenade, Hand, Practice, Mk. 2`` were too similar and the most effective way to prevent the errors was to have a completely different designation.

 Initially there is little to differentiate between the Mk. 2 Practice Grenade and the M21.  They both used the same bodies.  The M21 used the M10A2 or M10A3 fuze mechanisms.  In February 1945 the M205 fuze mechanism was developed specifically for the M21 grenade.  The M205A1 replaced the M205 in 1951 and in 1954 the M205A2 began to be used. 

 In the post war years, the bodies of the M21 were purpose made rather than utilizing bodies from fragmentation grenades.  The bodies are cast iron with an enlarged unthreaded hole in the bottom.  The hole is chamfered to assist in placing the cork in the bottom.  The fragmentation pattern is also different than live grenades.  The fragments are more pronounced and are quite rounded.   The top is threaded to accept the fuze mechanism which could be either the M205A1 or M205A2.  It appears that a single supplier was used to manufacture this type of body.  The bodies are marked RFX which is Richmond Foundry & Mfg Co. of Richmond VA.

 The grenades are painted light blue but the earliest versions may have a darker blue than normal.  There are no other painted markings.

 The grenade can be reloaded many times so long as the body remains undamaged.  Reloading consisted of replacing the fuze mechanism and inserting a paper or plastic bag containing 21 grains of black powder and plugging the hole in bottom with a cork.


 

Foreign Mk. II Types

Austria, HG 57 Austria HG57 Practice Germany DM28 Israel
Norway Norway M21F1 Portugal ?? South Korea A3

Body Markings found on Mk. II, Mk 2A1 and M21 grenades

AA AA AF AF AR AR Co
     
A A       BS
   
C---Crane C---Crane C---Crane C---Crane    
     
DC D       G
         
H          
   
ID or AH ID or AH L PA    
     
RFX---Richmond Foundry RFX---Richmond Foundry RFX---Richmond Foundry      
 
S S S S SM  
   
OKK V WEC U    
         
???          
           
           
           
           

Fuze Markings found on Mk. II, Mk2A1 and M21 Grenades

         
M6A2          
       
M6A3--RT M6A3--RT        
       
M6A4C M6A4C---PMC        
         
M10--- PA          
       
M10A1---Kodak M10A1---AFCO        
M10A2---Kodak M10A2---Kodak M10A2---FLI M10A2 M10A2---Kodak M10A2---FLI
 
M10A2---FLI M10A2---Kokak M10A2---Kodak M10A2 M10A2 Kodak  
M10A3---TE M10A3---FL M10A3---EK Eastman-Kodak M10A3---EFM M10A3 EFM M10A3 Shamrock
M10A3 PMC M10A3---UAMCO M10A3---CHE M10A3---CHE M10A3---Kodak M10A3---OTM
     
M10A3 remarked M10A3 Remarked M10A3 PMC      
       
M204---RT M204 PA        
         
M204A1---UCH          
     
M205A2---SGK M205A2---OPI M205A2---SGK