“The 155 mm Gun Motor Carriage M.12, attached to the 103rd Infantry Division, U.S. Seventh Army, was called upon to blast pillbox defenses in the Siegfried Line. The M.12 could carry 10 rounds on board. Besides those 10 rounds, it was designed to work in tandem with an accompanying M30 cargo carrier, which could carry an additional 40 rounds plus the gunnery crew for the M.12. The M.12 came with a big spade which was to be lowered into the ground at the rear to absorb the recoil. Only 100 were built. 99 made it through the war with 1 taking a direct hit.
This picture was taken in Niederschlettenbach, Germany, in 20 March 1945 and released by Field Press Censor three days later in 23 March 1945.”
Source: Signal Corps Photo ETO-HQ-45-22003
The Field Artillery Board were very pleased with the T.6 reporting that it was superior in mobility and maneuverability to other weapons of a similar caliber. For example a tactical test of moving the gun from firing position to firing position over a distance of six miles took thirty-five minutes with the T.6 against three hours for moving the some gun on a wheeled-mount towed by a tractor.
Standardization of the T.6 as the M.12 was approved at the end of August 1942. In the interim it appears that production of these vehicles had already commenced at the Pressed Steel Car Co., no official authority for this action has been traced. The first series vehicle came off the production line in September, 50 being completed by November, and a further 50 by March 1943. It could be that Ordnance Department, knowing of the opposition by certain Army Ground Force Generals to the whole concept had decided to force their hands with a fait accompli. On the other hand it may have been a genuine error by the manufacturing concern, on incorrect report, or even documents that went astray. Whatever the truth, the impression one gains thereafter is that whilst the Army Ground Forces had been forced to accept the M.12 they tried to delay using them for as long as possible. A few were put on extended tests, but the majority were only used for training or kept in storage for over a year.
Towards the end of 1943 reports had arrived from overseas regarding the use (by both the Russians and Germans) of big guns to fire point blank at defensive positions, impelled the Armoured Board to recommend immediate production of gun motor carriages for medium and heavy artillery. Even then, with the mass of evidence in favour of heavy guns being self -propelled the Army Ground Forces disapproved of the recommendations pertaining to them, stating that the existing M.12’s would meet all anticipated requirements for 1944.
By February 1944, every change and modification having been finalized for the M.12authority was given for Baldwin Locomotive to rebuild seventy-five vehicles. This gave sufficient vehicles to equip six Battalions each consisting of three Batteries of four guns with three spare. Rebuilding of seventy-four vehicles was completed by May 1944and by the end of July1944 shipment to the battlefronts overseas had been effected.
The M.12 differed from the pilot T.6 very little. The main differences being the later type of vertical volute spring suspension fitted with the trailing return rollers. A rudimentary gun shield for the gun layer, and a winch operated recoil spade. Ten shells together with charges and fuses were carried. The shells were accommodated vertically in recesses in the floor of the gun comportment. Two charges were secured centrally behind the gun, the remainder of the charges being located in racks beneath the two gun crew members seats at the rear of the left hand sponson. A further two gun crew members were provided with seats formed from the riser of the bottom step fitted between the arms of the recoil spade. On the underside of this seat the vehicle tarpaulin was stowed, and the footrest was formed from the lid of a carbine box. The spade was raised by means of a hand operated winch on the right hand fuel tank cover, and retained in position by a tie rod each side. Folding chocks were carried on the R. H. front track guard and used to stop the vehicle moving forward on counter recoil.
The reason for the brackets attached to the rear bogies is obscure. Some photographs appear to show wedges driven in between this and the track and it is suggested that they might be to stop the track jumping off the return rollers when the gun was fired. It could be that they were to relieve sheer stresses on the rear bogie, or act as supports for the sponsons.
One of the items requested during the rebuilding were sand shields otherwise there were no noticeable differences. A canvas cover was designed to fit over the gun compartment to protect the crew in inclement weather, but it is not thought that this ever become standard issue, in view of the fact that should a leak occur in the exhaust system it would be extremely dangerous for the gun crew.
Considering the obsolete type of gun utilized, M.12’s proved the advantages of the heavy Self-propelled gun. Its life however was very limited. The T.83 which utilized the for more modern 155mm gun M. 2 on a wider and longer chassis with Horizontal Volute Spring Suspension and 23″ tracks started coming off the production line in February 1945 and standardized in May 1945 as the M.40. At the same time the M. 12 was reclassified as Limited Standard, being declared obsolete in August 1945. It is of interest to note that from the time the pilot was recommended the T.83 took exactly one year to standardization being approved. The only known remaining example of the M.12 is retained at Aberdeen Proving Ground, Maryland.
Excerpt from a BattIe Ground report on the M.12
“Bottle of Siegfried Line” – battle of movement ended temporarily when the U. S. First Army reached the German border. The battle of the Siegfried line began. During this battle the battalion had a dual role: as on Artillery battalion delivering supporting fire, and as a siege gun reducing pillboxes and other fixed fortifications in the area. It is not possible at this time to give a detailed technical account of the use of the M.12 as a siege gun. Most of the pillboxes’ destroyed or neutralized by the battalion are still on the other side of the frontlines. Some general observations can be mode even now, however.
When the mobile phase of the campaign ended with the investment of the Siegfried Line ‘B’ battery was detached from the battalion and attached to the 9th Infantry Division for the specific purpose of direct fire against pillbox missions in addition to its regular artillery work for the 3rd Armored Division .
From 15th to24th September, thirty-five direct fire missions were assigned to the battalion. Of these twenty-eight were pillboxes and seven were fortified houses or observation posts. Sixteen of these missions were completely successful. On each of these missions complete destruction of the pillbox, penetration, or direct surrender to the fire of the M.12was accomplished. On the remaining nineteen missions varying degrees of neutralization were achieved. In most of these latter cases it has been possible to occupy the pillboxes or other structures on which the fire was delivered, but from prisoner of war reports it is concluded that casualties due to concussion and chipping of concrete occurred in all cases. An overage of ten rounds were fired on each mission.
Based on the experiences so far gained we believe that the M.12 suitably employed, will destroy, penetrate, or knock-out of action pillboxes of the Siegfried Line type . The projectile produces casualties and lowers morale of the pillbox occupants. No penetration of the heavy 14″steel cupolas which the better type pillboxes have are known of. It is also difficult to penetrate the best type of concrete, but in some cases seven feet of concrete were penetrated fairly easily.
The optimum range for the pillbox work would appear to be between 1000 and 2000 yards. At this range there is very little loss of accuracy or muzzle velocity, and the crew are out of range of much of the enemy’s small arms fire. Pillbox attacks should be closely coordinated with the supporting infantry and tanks so that neutralizing fire maybe delivered on the pillboxes while the M.12 is shooting for destruction. Most of the missions were fired by individual pieces, but perhaps massing the simultaneous fire of several M.12′ s would greatly increase the concussion effect as well as the shattering and penetration of the concrete, thus conserving ammunition.
Road marches of 200 miles have been accomplished in one day and the full track carriages has also made possible cross country mobility.
