Ammunition A completely new ammunition family, comprising shells, fuzes and cartridges, was designed for Abbot's L13 gun, designated "105 mm Field" ("105 mm Fd"). It is
separate loading cased charge ammunition (shell and cartridge loaded into the gun separately) with electrical primers, in contrast to the widely used semi-fixed US 105 mm M1 type ammunition (called "105 mm How" in UK service), which uses percussion primers, and has shorter shells. There were two versions of 105 mm Fd ammunition. Mark 1, which was used initially, had a UK-produced 105 mm How shell, mostly US pattern fuzes and reduced charge 105 mm Fd cartridges with their electrical primers. Mark 2 adopted a new projectile design, including an improved lethality
high-explosive (HE) shell (heavier with more HE) and full charge cartridges. Its shell types include HE, Smoke, Coloured Marker (Red and Orange), Illuminating, and
HESH for direct fire against enemy armoured vehicles. Direct Action, Controlled Variable Time (CVT) and Mechanical Time (MT) fuzes were available for HE and Coloured Marker shells. Initially, there were three cartridges. Sub-zones 1 and 2 were only used to provide short-range in high angle fire and were soon replaced by a plastic spoiler slipped over the shell
ogive. Normal cartridge gave charges 1–5, each bag being a different colour in accordance with established UK practice, Mark 1 normal cartridge only went to charge 4. Both marks had charge Super, a single charge cartridge, although the charge was reduced in Mark 1. Charges 5 and Super used extended "bags" that projected beyond the metal cartridge case. The 105 mm Fd uses double (often internationally called triple) base propellants designated N in UK service instead of the single based FNH propellants favoured by the US. The 105 mm Fd Mark 2 is still used with the
L118 Light Gun.
Gun Maximum range with 105 mm Fd Mark 1 ammunition was 15 km, the Mark 2 gave 17.4 km. Maximum rate of fire was 6–8 rounds per minute with 40 rounds carried in the vehicle. The gun was able to elevate to 70 degrees and depress to -5 degrees, sufficient to engage enemy AFVs if necessary. Traverse and shell ramming were powered by electrical servo mechanisms, elevation and cartridge ramming were by hand. Due to the number of charges and its compact turret, the Abbot did not have calibrating sights. Instead, the sight mount had both Tangent Elevation (TE) and Angle of Sight Scales with a separate Gun Rule to convert range into TE, corrected for the muzzle velocity variation from standard. The dial sight had all scales internal, illuminated and viewed through a single eyepiece.
Communications The Abbot was fitted with both line and radio
Larkspur B48, then
Clansman UK/PRC 352) communications to its battery command post, which used the Apparatus Loud Speaking No. 23, this enabled the gun No. 1 to acknowledge his fire orders merely by clicking his pressel switch. Initially, it also used induction loop communications for the turret and external crew. Shortly after the Field Artillery Computer Equipment (FACE) entered service in the early 1970s, the Gun Rule was removed and the Artillery Weapon Data Transmission System (AWDATS) installed. AWDATS displayed firing data transmitted from FACE in the battery command post via line or radio.
Mobility The Abbot was able to swim across water, using a flotation screen fixed around the hull, raised to provide buoyancy. The action of the tracks was sufficient to drive it forward at about (see also
DD Tank). Each Abbot was supported by an amphibious
Stalwart High Mobility Load Carrier with additional ammunition. ==Service history==