18pdr guns developed at the end of WW1 introduced the platform. At that time it was intended for use when the gun was being used in close support of an infantry advance so it could traverse and fire at the numerous bunkers the Germans used in late WW1 defences. However the weapon known as 18pdr fieldgun MkIV on box carriage Mk III wth firing platform, was too late for war service. It was exported to Estonia, Ireland, Latvia and China. British army guns were converted to vehicle tow later.
The MkIV on box carriage MkIII but WITHOUT platform was in use during the last year or two of WW1.
Unlike the "pole trail" of the most common 18pdr field gun Mk 1 on carriage Mk 1 or carriage II the carriage MkIII was a box trail and this was the weapon converted to the 18/25pdr. Indeed the box trail of this gun became the model on which the 25pdr trail was based. The pole trail was abandoned for a box type after the MkII type because it was realised that although quick and easy to pick up and turn, it was not sturdy enough for the prolonged firing typical of WW1. No pole trail 18pdrs were converted to the 18/25pdr. Only Mk III trails. The 18pdr guns used by Indian and Commonwealth forces in the early part of WW2 had the common pole trail. These saw service in the Middle East and North Africa. However as more and more 25pdr guns were supplied to the British army they passed on the 18/25pdrs to Indian and Commonwealth forces.
One has to be careful not to get confused in early North African battles when first the origional 18pdrs were used by those forces, (They usually took them with them) then later the 18/25pdrs passed on by the British. And finally fully fledged 25pdr guns.
Note also that due to the extreme shortage of 25pdrs many of the Commonwealth forces were using motor tow conversions of the WW1 4.5"howitzer. Where this was the case, they were always accompanied by some 18pdrs in the battery because the 4.5" had no anti tank capability at all. But if they had been re-equipped with the 18/25pdr to replace the 4.5" howitzers, the ordinary 18pdrs were returned to depot.
In the between the wars era it was realised during exercises that the platform allowed the gun to be traversed quickly in order to engage tanks. Therefore the idea was carried over to the 25pdr. This enabled the 25pdr to be much more effective in an anti tank role than most field guns.
But certainly all the 18pdr gun types still in service at the time they were converted from horse tow to vehicle tow, were provided with the traversing platfor….including the somewhat rare 18pdr Mk IV on carriage Mk V with a split trail. It was intended this gun would replace all the earlier models, but for financial reasons it did not and besides, there was a glut of almost new or little used 18pdrs.
The use of the gun without the platform could occur if it was deployed in emergency and there was no time to place the weapon on it. Or if the gun was emplaced in a position where it was not expected to be required. Alternatively, it could have been lost or damaged!
The 18/25pdr was still in wide use throughout most of the campaign in Malaya and Burma as was the 4.5" howitzer. It was very late in the war before there were enough 25pdrs to replace all the weapons in the Burma campaign.
In 15mm QRF have a 4.5" howitzer. I made the master for them.
The 3.7" mountain gun modified for truck tow and with a shield similar to the 6pdr anti tank gun was also quite common in North Africa, the Middle East and Burma. especially with Indian troops. That is another master I did for QRF and available from them. Some of these apparently received a traversing platform too, but it was not common.
