The M7B1 is a so-called 'self propelled gun' and was produced from 1944 by the Pressed Steal Car Company.  The Priest has the same underside (“chassis”) from a Sherman M4A3 tank, so also the same engine, powertrain etc. The M7B1 had a Ford GAA V8 tank engine with a volume around the 18 litres and use minimally 4 litres gasoline for 1 ½ mile.  Not exactly an economic tank, but possible good for the stamps at the gasoline station!  In the second world war the fuel consumption  wasn’t an issue, as long as it runs. That’s why there are 4 gasoline tanks in the Priest. With the full capacity of 670 litres the Priest could drive 85-125 miles on 670 litres. If you start the tank “cold” and drive away. The Priest would use after 50 meter around 30 litres gasoline (as a small indicate).  Enough about the fuel consumption, because with this engine you get 500 break horse power at 2600 RPM and 1100 Nm at 18000 RPM back.

A little bit of the history of the Priest: 
Before the M7B1 was produces there was one type earlier named the M7.  This one was used by the USA and G-B. The Americas used before the M7 was designed, the 75mm and 105mm Howitzer assembled on a half-track (GMC:  Allow Motor Carriage).  But the American army wanted a Howitzer on a vehicle with only tracks therefore they designed a vehicle with mainly parts from tanks in 1941  There were two prototypes built, The were named T32. After testing these prototypes they decided tot take the M7 GMC in production. What also nice is to point out is that the Britisch troops named this vehicle Priest, because of the .50 machinegun pulpit. This pulpit looks unmistakably a lot like a pulpit in the church.

M7B1 Priest:
M7B1 Priest came later in production then the M7 and was put together with mainly parts from the M4A3 Sherman, but still looks a lot like the M7. The M7 had been put together only with parts from the M3 Lee / Grant. The armament and garrison of the M7 is the same as the M7B1. As I already pointed out in the introduction the Priest has a Ford GAA V8 engine.  This engine supplied his power via a double clutch plate throw the drive line to the transmission house. The transmission used was the synchromesh type. It had 5 gears forward and 1 reverse. The synchromesh were actual unnecessarily for the Ford GAA V8 because by this type of engine you already can shift gears by 300 RPM. Why would the used the synchromesh type you think then?

Why they used the synchromesh type is because before the Ford GAA V8 tank-engine was developed they placed a radial-engine Continental R975-C1 in the Priest. This one was based on a 9-cylinder air-cooled airplane engine with a output of 450 bhp. The big problem with this engine was that this engine need to be on high revs to have this power. This airplane engine was namely built for an constant rev, so if it is used in the tank it needs to be on high revs to have some useable power.  That is why they used the synchromesh transmission because they had to schift on a relative high rev

Function of the Priest:
The M7 and M7B1 Priest were used by the American and British armour divisions. The advantage was that the vehicles were flexible and they could gave the tanks of the armour divisions on every desired moment artillery support. The Priest was in action in North-Africa, Sicily, Italy, Normandy, and the further fights at the west front. After the invasion in Normandy the British Priests were however replaced by the Canadian Sexton. 

The Priest pointed out to be a very effective vehicle. That’s why it is frequently used after the  second world war.  The M7B1 is also used in the Korean war in the begin of the 50’s. The M7B1 were modified to have a larger shooting range. This was simply achieved to raise the howitzer canon and ad an extra segment to the pulpit. This modification is later indicated as the M7B2. 

Technical information:

Priest M7B1
22.700 kg
7 (Commander, Driver, gun crew)
Ford GAA, 8 cilinders, benzinemotor, 450 / 500pk
5 forward 1 reverse
25 miles/h (40 km/h) on the hard ground
15 miles/h (25 km/h) on the soft ground
Road radius
140 - 200km
Length : 6,02m
Width : 2,87m
Height : 2,95m
Main:105mm houwitzer M2A1
Secundary: .50cal M2HB Machine Gun, 3 .45 Submachine guns
105mm - 69 granaten
.50 - 300 patronen
.45 - 1620 patronen
108 mm max
3/44-2/45: 826