Tracklink Article -  SP-70 Self Propelled Gun

This was originally published in Issue 113 (Autumn 2022) of Tracklink, the magazine of the Tank Museum.  However, the photos which accompanied it are owned by the tank Museum, so I have replaced them with another photo from the public domain

The SP-70 155mm Self Propelled Gun

The SP-70 (also known as the PanzerHaubitz 155-1 and the Semovente 155mm) began in the late 1960s as an Anglo-German project to replace their existing US-made M109 SP Guns with a more advanced gun with higher rate of fire and better range.

Italy then joined the project, and it may say something about the large multinational defence projects common in the 1970s that project managers estimated that a third country joining would push the in-service date back six months and increase costs by 11.7%, mostly from extra project management and an additional set of technical evaluations.

As common with such international projects, work was parcelled out between the participating countries with Germany being responsible for the chassis and powerpack while the UK produced for the turret and Italy developed the gun support equipment (power elevation, recoil system etc)

The system definition study was completed in 1971, and at that point the system was expected to enter service in the late 1970s or early 1980s. A 1972 costing gave a price per vehicle of £148,682, or around £3.1m in 2022 prices

The design that emerged had a large turret mounted on a tank-type chassis with the engine in the rear, which prevented rounds being passed manually at low level through a rear hatch as they were on the existing M109.

The chassis was not that of the German Leopard I, as sometimes claimed, though it did use a significant number of Leopard components and its 8-cylinder MTU engine was based on a shortened version of that of the Leopard. It was fitted with seven roadwheels, a torsion bar suspension and used Leopard I tracks.

The vehicle was to be armoured against 7.62mm AP and shell fragments, with the frontal arc protected against 14.5mm at 100m. The original proposal was for steel armour, but this was changed to aluminium to keep the weight down. Since it was expected to fight on a nuclear battlefield, a full NBC system was required.

The core of the vehicle was the 155mm gun, which had a range of 24km with standard rounds, or out to 30km with rocket assisted extended range projectiles. As most of the casualties from artillery bombardment are inflicted in the first few seconds, before troops in the open can take cover, the specification required a "burst capability", firing the first three rounds in ten seconds to inflict maximum damage during this time.

This was achieved by pre-positioning shells in the breech, on the rammer and on the ready use tray. After this, it could continue to fire six rounds per minute while shells remained in the mechanical autoloader magazine in the rear of the turret. This held 32 rounds, any of which could be selected for loading into the gun.

It was reloaded by a pair of external mechanical arms which could pick up shells from a pile on the ground and load them into the magazine through a port in the rear turret wall. From there a round could be moved on into the breech for firing, all without human intervention.

The main advantage of the system was that it allowed the heavy (43.6kg) shells to be loaded without a large loading crew who would slow down as they became exhausted. The lighter 12.6kg charges were much simpler to handle manually.

This shell replenishment system could handle around four rounds per minute when working properly, so the vehicle dropped to this sustained rate of fire once the rounds in the magazine were expended and the vehicle was depending on external ammunition during a long bombardment.

An emergency manual system was available in case the shell replenishment gear failed, using a chute in the front of the hull. However, this was actually slower than simply passing rounds through the large rear doors of a conventionally designed SP gun.

The vehicle had a crew of five, with the driver in the hull. The commander / crew chief, gunlayer and shell loader / magazine operator sat in the turret to the right of the gun, with the charge loader to the left.

A total of 12 prototypes were created, including five "Phase A" prototypes used for development and trials.

Six of the seven "Phase B" prototypes were formed into a six gun Joint User Trials Battery, with two guns manned by soldiers from each of the UK, Germany and Italy.

The last prototype was used for climatic trials, then passed to Germany (who developed the chassis) for maintenance studies once these were complete.

Cold weather trials were seen as essential, and were held in Norway from 1984. Hot and dry climate trials were seen as highly desirable and were planned for Sardinia, which retrospectively seems rather a low bar, given how much time the British Army actually ended up spending in the much more extreme climates of Iraq and Afghanistan.

Hot and wet climate trials were only seen as necessary if sales to non-NATO countries looked possible; as this never looked likely, these were never added to the trials programme.

Initial automotive trials were reasonably successful, which was not surprising given the chassis was based on well proven components. Other aspects proved less positive. The hand controls for the gun laying system were found to be awkward to use, but more importantly, the mechanical shell replenishment system proved very problematic.

It performed badly in the cold weather trials, with the mechanical arms icing up and freezing in the stowed position if not used daily, did not always function reliably and was notably sluggish when operating in the cold conditions.

Indeed, the shell replenishment system could most charitably be described as temperamental even in temperate conditions; it depended on multiple microswitches operating correctly, and even one being out prevented the system working properly. With the back-up manual system being slow and awkward, this threatened the viability of the entire project.

As a result, the project was cancelled in the mid-1980s. Instead, the British Army adopted the AS-90, developed by Vickers as a private venture in anticipation of the SP-70 project failing. This mounted the same gun in a more conventional front-engine SP gun chassis, with a crew of 6 and ammunition loaded manually via a large rear door.