From the Vault: Comparison of Performance of 75mm and 76mm tank gun ammo

Today we present a British report from 1944 comparing the performance of 75mm and 76mm ammunition used by the different variants of M4 Sherman tanks and British vehicles equipped with the QF 75mm gun (Cromwell, Churchill.)  This report was photographed by a friend of the site who was doing some archive digging over in the UK.  The armor penetration figures are not particularly interesting since these figures are quite well known.  Of more interest is the data on the H.E. rounds.  While it is generally stated in most sources that the 75mm gun had a superior H.E. round compared to the 76mm gun, few books give actual data as to how these H.E. rounds differed. For your reading convenience, we have provided a transcript of the report as well as images of the original photos.

Army Operational Research Group Memorandum No. 415

Comparison of the Performance of 75mm.  and

76 mm. Tank Gun Ammunition

GENERAL

1. This memorandum is primarily a comparison of the H.E. shell 75mm. M48 and 76mm. M42 A1. As, however, comparison of the H.E. shell only does not give the full picture, figures for the performance of the A.P.C.B.C./H.E. projectiles against armour plate are included.  The 76 mm. is inferior in performance against personnel, but superior against armour, and an attempt has been made in summing up to assess the relative merits of the guns for general use.

COMPARISION OF H.E. SHELL

2. Details of Shell. The 75mm. M48 is longer and heavier than the 76 mm. M42 A1 and has a greater capacity.  Both shell have the same fuze (M48) so that no differences in performance arise from the fuzing.  Fragmentation particulars are available for the 75 mm. M48 but not for the 76 mm M42 A1.  However, a comparison of the 76mm M42 A1 with the 3″ M42 A1, for which fragmentation data are available, shows that these two shell are practically identical in external appearance, weight, capacity and fuzing; it has, therefore, been assumed that their performance will be identical for all practical purposes.  Details of the three types of shell are shown in Table I.

Table I.

3. Results of Trails O.S.R.D. Reports on Fragment Velocity and Panel Penetration Parts I and IV (SR 7/44/61 and SR7/44/528) give details for both the 3″ M42 A1 distribution obtained from all fragmentation experiments for the same two shell.  The distribution is expressed as the percentage number of fragments exceeding a certain weight out of the total collected on a number 4 screen, i.e. all fragments exceeding a few grains in weight.  These figures are summarized in Table II.

Table II

It will be seen that the thicker the target the greater the superiority of the 75mm shell becomes; against personnel the difference will be much less marked.  It should also be pointed out that since the 76mm gun has a higher muzzle velocity, the difference in the resultant fragment velocity of fragments from 75mm and 76mm shell burst in flight will be less than in the static trials, and therefore the difference in performance will not be so great as the above table indicates, although it will still be substantial.

4. Vulnerable Areas. In order to assess the performance of the shell against personnel a comparison has been made on the basis of vulnerable areas against men in the open. The calculations are based on the experimental fragment distributions and velocities referred to in the last section, but to complete the fragment distribution an estimate of the number of smaller fragments has been made by comparison with other shell of similar capacity.  The fragment zone of the 76mm shell in flight may be expected to be a little wider than that of the 75mm shell because the higher striking velocity and lower velocity imparted by the detonation would lead to a greater throw forward and spread of fragments from the former shell.  As data for an accurate estimate of the fragment zones are not available and in order to avoid hiding any genuine inferiority of the 76mm shell, the same fragment zone of 30 degrees has been taking in each case.  the resulting figure for the superiority of the 75mm shell may therefore be regarded as a maximum and the vulnerable areas as relative rather than absolute values.  The results are given in Table III.

Table III.

Vulnerable Areas against men in the open

COMPARISION OF PERFORATION PERFROMANCE

5. The following figures are given for the thickness of homogeneous armour plate penetrated at 30 degree angle of attack by A.P.C.B.C./H.E. shell.

Table IV.

The superiority of the 76mm gun for this purpose is very marked, its penetration at all ranges being 35-50% greater than that of the 75mm gun.  The value of the gun against tanks cannot be assessed in the same terms, a 50% increase in penetration of the 76mm A.P.C.B.C. shell may mean considerably more than a 50% increase in effectiveness in service.

6. The 76mm gun also fires a composite rigid A.P. shot. Its performance is compared with that of the 17 pr. D.S. shot in O. B. Proc. Q2644, an extract from which is given below.

Table V.

COMPARISION OF GENERAL PERFORMANCE OF 75MM AND 76MM GUNS.

7. While the difference in performance of H.E. shell is merely one of degree, in that the same effectiveness against personnel can be secured by the expenditure of a few more of the less effective shell, a decrease in the range at which penetration can be secured is a disadvantage which cannot be overcome.

A.O.R.G.

9th October, 1944.

JL