Haubits FH77-Cedar Herald Index

() or FH77 is a Swedish 155 mm howitzer, developed and manufactured by Bofors. It is also colloquially known as the Bofors gun in India. There were several versions, the original (sometimes referred to as Haubits 77 A) with a 38 calibre barrel and sliding block mechanism, the export version FH77 B version with a 39 calibre barrel and an interrupted ogival screw breech. For the demonstrator of the Archer Artillery System, some FH77A were modified into FH 77 AD L/45, while the series production were FH77Bs rebuilt into FH77 BW L/52. The carriage was also used for the "", used in the Swedish coastal artillery.

Design and development

History

In the 1960s, Sweden started to look for a replacement for the French Obusier de 155 mm Modèle 50 (Haubits F). The American M109 self-propelled howitzer was offered and tested. Though the price was low, the Swedish Arms Administration found that the high maintenance costs, the low rate of fire and the limited mobility of the M109 made it worth the effort to develop a domestic howitzer.

Haubits FH77

The requirements for a new gun would be: High mobility. High momentary rate of fire.

Haubits FH77

The result was a compromise between a more expensive self-propelled howitzer and a less mobile conventional towed howitzer.

Haubits FH77

The FH77 was the first field howitzer featuring an auxiliary power unit to make it self-propelled for tactical movement.

The rate of fire was, at the time, exceptionally high for a 155 mm howitzer. The FH77A (which uses semi-fixed ammunition) could fire 4 rounds in 9 seconds, or 6 rounds in 25 seconds. In a sustained firing role, it could fire 6 rounds every two minutes for 20 minutes (i.e. 3 rounds per minute).

In order to use standard NATO ammunition, the FH77B was developed. While the sliding-block worked well with the cased charges acting as a seal, it was decided that bagged charges required an interrupted screw breech. This, combined with the slightly longer barrel, resulted in a slightly improved range but also a lower rate of fire. At the same time, the petrol-fueled auxiliary power unit was exchanged with a diesel-fueled one, allowing it to use the same fuel as the towing vehicle.

Driving and deploying

The dedicated towing vehicle for the FH77 was the Scania SBA111 (Tgb 40). The truck was equipped with a crew compartment behind the driving cab and a HIAB-crane for ammunition handling. The howitzer's auxiliary power unit can be started and controlled by the driver of the towing vehicle to give an extra boost during off-road driving. The maximum towing speed is 70 km/h (45 mph).

The FH77 is manoeuvred by the gun layer, controlling the torque of the two main wheels through a joystick. Speed is regulated by changing the auxiliary power unit's revolutions per minute. The howitzer is deployed by spreading the trail legs, raising the castor wheels and driving the howitzer in reverse to anchor the recoil spades.

Auxiliary power unit

The FH77A is powered by a Volvo B20 auxiliary power unit, which gives the gun a top speed of 7 km/h. The engine is connected to three hydraulic pumps, of which two are linked to the wheels and one is used for a traverse, elevation, ramming and ammunition crane. The fuel tank could hold 40 litres, with two extra 20L jerry-cans as a reserve in front of the gun layer's position. The FH77B has the same configuration, but is powered by a Mercedes-Benz diesel engine.

Crew

The crew consists of 10–14 men. The minimum crew setup would be 4 men; commander, gun layer, loader 1 and loader 2.

The commander directs all the activity of the crew from a platform to the left of the gun layer. The layer sits on the left hand side of the gun, operating the fire control computer and driving the howitzer when in self-deployment mode. Loader 1 is located to the right hand side of the gun and is in charge of supplying the shells from the loading table in front of him. Loader 2 and 3 would be working on the ground, providing shells to loader 1 by means of a hydraulic crane and loading cases in the loading trough. Loader 3 is normally the driver of the towing vehicle.