The British preferred to tow the howitzer in the firing position, but to do this and not damage the balance springs (elevation mechanism) they added the clamp seen in the photo.
To deploy, the clamp is unstrapped, swung down onto the axle and then screwed to tighten in place, thereby allowing the howitzer to be towed in the firing position, without risk of damage to the balance springs.
75mmPack-Brit-AB-Axle-Brace-Mod.jpg (62.3 KiB) Viewed 334 times
In summary therefore... British Airborne use of the 75mm Pack Howitzer M1A1 on Carriage M8
Replacement Tow Eye (US Made originals snapped frequently) Axle/Elevation Brace (allowed weapon to be towed in operational areas "ready to fire" without damage to the elevation mechanism) Footman loops and brackets welded to rear trail (carriage) to allow sight box, handspike, range posts and other items to be carried on the Howitzer rather than by the crew. Axle retaining clamps (to stop the axle rotating and coming off during towing - US Locking pins snapped frequently).
Sides given when looking towards the target from the rear of the howitzer.
LEFT side - Ammunition Handling, Laying and Loading RIGHT side - Breech Open/Closing, Firing REAR - Gun Commander, Giving Orders, Inspecting ammunition (fuse and charge) before loading, Traverse adjustments which are greater than those available using the axle traverse wheel using the handspike to move the trail.
Will see what other photos I have which can better illustrate the above.