Broadly speaking, there have been four generations of the Land Rover-based Marshall Field Ambulance.

First Generation
The First Generation utilised an extended and raised body on either a Series II/IIA or, less commonly, Series III 109". These were in production from the late Fifties right up to the early Eighties and were based on the MoD specification 109" of whatever Series was in production at the time.

Second Generation
The Second Generation was based on a rebuilt 101 Forward Control and had a comparatively short production run. All 101-based Ambulances were built during 1981-2 using factory-remanufactured 1976 vehicles, 101FC production having ceased in 1978.

Third Generation
The Third Generation might be considered a sort of stop-gap measure as Marshalls didn't have it all their own way. Based on the 127" chassis (an extended 110 chassis, the modification being carried out by in-house by Land Rover Special Vehicles), there are two versions of the body - that of Marshalls and Locomotors. While both being very similar, Marshalls managed to carry over the rounded corners at the front of the body, echoing the aesthetics of the earlier version, while the Locomotors body adopts a more slab-like approach.
The 130 is a quantum leap from the 101, which in turn is a quantum leap from the 109. With the 127-based version, the process of evolution is very clear to see. For a military vehicle, it is also surprisingly civilian - this is because it's not based on an MoD-specification vehicle, but one built by LRSV. Like the V8 110s the MoD used for special applications (prior to the adoption of the 300Tdi), the basic electrical system, switchgear, lighting, dashboard, cab and seating are normal factory build.

Fourth Generation
The current version, the Third Generation, is based on the military-spec Defender XD130 (and, in this guise, is also known as "Pulse" or, less accurately, "Wolf"). Hopefully someone will be able to clarify whether there have been different versions of this design, particularly as the base vehicle has developed from the original Land Rover 127 to the current XD130, using a purpose-built 127" chassis.

The first two generations are well represented within the ranks of EMLRA, including an armoured variant for use in Northern Ireland, and some 3G 127-based examples have started to appear. Alas, no-one has yet been able to obtain an XD130 - but it probably won't be too long as they are now beginning to appear, although with prices at the thick end of £15,000 they won't be a common sight for some time. In early 2003 a Club-based consortium nearly secured a desert-specification ex-works demonstrator, but unfortunately some rather more heavyweight commercial concerns found out and immediately whisked it away to an undisclosed destination.