"a FO canīt use its ability to call a bombardment while inside a vehicle"
The above statement strikes me as really quite odd as that is exactly where the Forward Observers worked from. Inside the vehicles. Both British and German FOs used armoured half-tracks. By the time of Normandy the British also had FOs working from inside gutted Shermans. In the case of the Sherman the main gun was removed and replaced with a large map table and extra radios while the gun was replaced with a wooden dummy. If you look at the Sherman knocked out in the main street of Villers Bocage, 1944, you will see that the splintered wooden gun is lying on the ground and the mantlet is wide-open and empty, the stump gun was blown out when the tank was hit by Wittmann.
As to the Dingo, they were basically an armoured jeep with the ability to carry a driver plus two in comfort, three at a squeeze, plus radios. They were primarily armoured car troop equipment (two Dingoes and two Daimler A/C per troop) but other units had them on an ad-hoc basis. The A/Cs had the 2-pounder gun for troop protection, the Dingoes had the radios. However I am quite sure an enterprising FO could find a Dingo if he needed one…
In the case of my late father's unit (86th Anti-Tank Gun Regiment, RA, part of XII Corps) the REME fitters badly wanted a fast armoured runabout to transport them and tools to repair jobs in Normandy. They found one damaged Dingo in a vehicle dump which had run over a Teller mine and lost the front axle while another was found which had been hit by a shell in the engine compartment. Both were recovered by the fitters and the front axle was removed from the shell victim and fitted to the mine victim. Now they had a very fast armoured runabout for doing repairs which they rated higher than their Universal Carriers. This was used for just a couple of weeks until a passing officer, noting that the Dingo was above their establishment, pinched the Dingo as his personal runabout. Dingoes were THAT popular.
Also used for FOs were M3 and M5 half-tracks and the White M3 Scout car. Similar vehicles were also used by the RAF to call in air strikes from 'the cab rank'. This later was a reference to London taxis being permanently on-call. The cab rank in this case being Typhoons circling about two to four miles back until a FO called them in.
In my late father's case the RAF FO was out of his vehicle in a trench, next to him, on the rear slopes of Hill 112 as Tigers and Panzer Grenadiers were assaulting the front of Hill 112. There was quite a delay and by the time the Typhoons appeared they were firing their rockets from above Dad's trench straight into the face of the attack about 800-1000 yards away. A little while later he heard this from the RAF FO trench: "Thank you for the close support… next time not so 
ing close!"
So short version, FOs can work from vehicles (recommended) or trenches.
Barry
