Avro Lancaster Serial Groups Specifications

Avro Type 683 Lancaster

Ventral Turrets

As originally designed the Lancaster was provided with ventral defence in the form of a Nash and Thompson FN64 turret, which was fitted to some early production aircraft. However, in common with all other periscope sighted ventral turrets, the narrow viewing angle made it almost impossible for gunners to acquire and track targets, and the few turrets which were installed were soon removed from service.

The ventral .50 inch (50 calib) was approved as Lanc Mod.925 during February 1944, and was one of a number of unsuccessful measures taken to counter night fighter attacks from below.

The growth of the Luftwaffe night fighter force was followed by an increase in the in the number of attacks from below, exacerbated from August 1943 onward by the introduction of aircraft equipped with Schrage Musik upward firing 20mm cannon. A number of responses were considered by Bomber Command including a free mounted ventral .50 calibre Browning machine gun, which was approved on the Lancaster as Modification 925 during February 1944.

The modification was very basic, consisting of little more than an enlarged bicycle seat for the gunner and a simple free mounted gun with open sights which fired through the ventral turret/H2S aperture. On aircraft with bulged bomb doors the mounting (often unpainted) was incorporated into the fairing at the rear of the doors.

Non-H2S fitted aircraft were sporadically equipped with the gun from February 1944 onward, although a clear plan for installation appears to have been lacking. The quantity of aircraft which actually had the gun installed is unknown and photos of the mounting with a Browning actually installed are very rare.

Serious problems quickly became apparent, as noted in the following V Group monthly newsletter for April 1944:- "With the gunner strapped in his seat it is difficult to follow the gun round on the beam; it is difficult for the gunner to get his head down behind the sight as it tends to push the oxygen mask upwards on the gunners face; and also considerable vibration is experienced on the sight when the gun is fired."

These problems, plus the gradually more widespread introduction of H2S saw the gun fall out of use quite quickly, although it does appear to have been retained on some aircraft until war's end (most notably in 3 Group).

The quantity of aircraft which actually had the gun installed is unknown and photos of the mounting with a Browning actually installed are very rare.

Notice on these aircraft the extra position in the eight person crew of Mid-Under-Gunner.