In October 1943, Headquarters, Army Service Forces
directed that a project be initiated to develop a bayonet
for use with the standard carbine. It was further directed
that several types of bayonets or adapters to permit the
adaptation of the trench knife as a bayonet for the car­
bine be developed and procured as early as practicable.
This project was initiated in the latter part of October
1943.

Three types of carbine bayonets were developed,
the Carbine Bayonet T4 had a clamp to fit over the front
sight and had a round cross-section blade 7 inches long
and 3/8 inch in diameter at the hilt, the Carbine Bayonet
T5 had a clamp to fit over the front sight and the blade,
which had a diamond shaped cross-section, was 7 inches
long and 1/4 inch by 3/8 inch at the hilt, last was the T6
Carbine Bayonet with clamp to fit over the front sight
and a knife blade 7 inches long and 3/4 inch wide, having
the same contour as the blade of the M3 Trench Knife
(fig. 196).

In order to comply with that portion of the directive
from Headquarters, Army Service Forces, wherein an
adaptation of the trench knife for use as a bayonet was
to be developed, the following described modified trench
knives were developed through the coordinated efforts of
the Ordnance Department and the Imperial Knife Com­
pany personnel.

The T8 Knife consisted of the modification of the
front guard and butt plate of the M3 Trench Knife. The
butt plate was so constructed as to have incorporated
therein a single catch. Before it could accommodate the
T8 Knife the carbine barrel required the addition of a
bayonet stud to be pinned to the barrel.  Upon inspection
of the T8 Knife it was found that if the bayonet catch
was accidentally depressed, the bayonet would come off
the carbine. This was remedied in the next model.

The Knife, T8E1, differed from the T8 in that a second
bayonet catch was inserted into the butt plate of the
knife. This knife, together with the new carbine front
band bayonet lug assembly described in a previous
chapter, permitted ready assembly and removal of the
knife to the carbine.

In January 1944 samples of the T4, T5, T6, and T8
Carbine Bayonets were sent to the Infantry Board for
inspection and test. Based upon the report of test of
these items (Infantry Board Report No. 1586), Headquar­
ters, Army Ground Forces requested that the following
be accomplished:

a.          The M3 Trench Knife be designated as Limited
Standard and its manufacture cease with the least prac­
ticable delay.

b.          The T8 Carbine Bayonet be standardized and
manufactured in lieu of the Trench Knife M3, inasmuch
as the modification in no way detracts from its use as a
knife, but instead enhances its value by making it a dual
purpose weapon.

c.          The catch on the T8 Knife to be the same as that
of the T8E1 which was merely demonstrated to Head­
quarters, Army Ground Forces personnel. (The model T8E1
incorporated a double catch which corrected the faults
found with the catch of the T8, as tested by the Infantry
Board.)

d.          The new front band bayonet lug assembly be
adapted to all carbines issued to Army Ground Force
Units.

e.          The Carbine Bayonet T8E1 be issued under the
same basis of issue as prescribed for the M3 Trench Knife,
with a priority of issue to those troops armed with the
carbine. The Knife T8E1 was standardized in May 1944,
and designated as Bayonet-Knife M4 (fig. 197). It is to be
pointed out that the Scabbard, Trench Knife, M8A1 is
usable with the M4 Bayonet-Knife.



-Chapter 7, Bayonets, Knives and Scabbards from the Record of
Army Ordnance, Research and Development Volume 2.