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American Mk.II Fragmentation Hand Grenade
U.S. Mk.II Evolution
The most recognized hand grenade design used by the U.S. Army from 1918 up through the 1960's. The Mk.II "Deuce" is arguably the most sought after piece of ordnance for American militaria collectors.

While there is much available documentation about the specific details of this grenade, the attempt here is to provide a simple side-by-side presentation of outward physical features as it evolved over its 45+ year lifetime.  Hopefully something of use to those new to the subject, and entertaining for the advanced collector as well.
(Some of these observations are not in agreement with other published data. My humble observations and conclusions.)

Mk.II Early Transition


The Mk.II hand grenade was born at the end of WWI, the child of the failed Mk.I design , when the basic lemon shaped body style of 40-segments in 8-columns of 5-rows with a grooved neck was established.
Shortly after, the body was further modified to the familiar shape which remained outwardly more or less the same for the rest of its service life.

As a starting reference, some subtle differences between the first Mk.II body (left) and its immediate successor (right) are worth noting:

A) The base was widened. The first Mk.II body had a very narrow base, just slightly wider than the fill plug.

B) There is a measurable difference in the overall height of the body. It seems later designs are about 0.08" shorter.

C) The "shoulder" profile is more angular, although this varies in degree.

D) Segment grooves tend to be wider and deeper, but there are exceptions.

Mk.II circa 1920 - 1930
Mk.II - Post WWI (circa 1920-1930)
An often overlooked period in the history of the Mk.II is from the 1920's thru the early 1930's.

Recognizable features are the short lever "cut-back" Mk.II fuze and the noticeable flat "shoulder" on the body. ("A"). Note, the verticle segment groove is not continuous from the body to the neck.

Color schemes vary from blackened iron, black or gray paint to red.
The red color (practice) was adopted from the French and German practice types. This pre-dates the early blue painted Mk.II practice grenade.
All have a 3/8" threaded filling plug in the base.

Mk.II 1942-1943
Mk.II  WWII 1942-1943
Sometime in the 1930's the body shape was changed slightly, now with a continuous vertical groove pattern. The fuze bouchon (body) was modified by eliminating the "cut-back" and the  safety lever lengthened.

Yellow was the color code for high explosive ordnance at this time and HE grenades were painted accordingly.  Understandably this was found to be an impractical color due to its high visibility to the enemy.
In 1942 the the color was changed to "olive drab" (OD) with a small yellow band. With many thousands of yellow grenade bodies in inventory they were repainted, green over the yellow.  
In this picture you can see the yellow paint showing through chips and wear spots on the OD bodies.

During this period the threaded fill plug in the base was no longer required, but phasing out that feature was not a high priority. There can be found yellow Mk.II's with solid and plugged bases, as well as later production Mk.II's with fill plugs.

Mk.II circa 1945
Mk.II  WWII 1944-1945

In the closing years of WWII the Mark II was produced with a solid base with the M10A3, or M6 series fuze (depending on the explosive filler used).
The yellow band around the neck of the body was standard.

The are numerous variations in the fragment and groove details that can be found, which seems to depend on the particular manufacturer.

Post WWI Mk.II Mk.II Post WWII
At the end of  the War the fuze lever & bouchon design were modified to a split-toggle pattern. The new detonating fuze for the Mk.II was the M204A1 (A2).
This was the primary defensive grenade used up to the Korean War.

Mk.II A1 ?
Although it useful for historians and collectors to identify grenades with the solid base as the "Mk.II A1", it is not entirely clear (to me) that nomenclature was ever an official military designation.

At left is a detail from the "Guidebook for Marines" published in December 1965. The designation here is "MK2" (No Roman Numerals) and is described in the text as still in use as "Limited Standard", being replaced by the M26A1 grenade.

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