Roberts was ordered to mount the 15" turret from the hulked Marshal Soult, and was shorter than the "Erebus" class due to lower powered boilers, and compact modern 3-drum boilers and turbine engines.
Unlike the earlier monitors which had been very bare above deck level, a large close fitting brisge and superstructure was added very close behind the 15" guns, and substantial tripod fore and main masts were rigged. In every respect, they looked like minature Nelsonclass battleships - a psychological advantage in battle?
Because it was realised that they would work bombarding shore targets, a very heavy AA armament was fitted to protect against shore aircraft attack. Quad pom-poms were added on each side of the main turret, and along cruiser lines, amidships four twin 4" AA were fitted in a square arrangement. An octuple pom-pom was added on the quarterdeck. AW type 281 was added to the mastheads, AR type 285 on the 4" HA/DCTs and AR type 282 on the three pom-pom barrage directors. Eight single 20mm Oerlikons finished off the armament. In 1943, six Oerlikon were replaced by twins of the same, AW type 279 replaced the type 281 and SW type 272 was added. The funnel was also heightened.
It was intended to send her East to clear the Japanese from the pacific islands, and eight single 40mm Bofors were added and a further two twin 20mm's were added.
Abercrombie was laid down later, to a modified design, to use Furious's second spare 5" turret. Larger accomodation spaces, remote control for the 4" and 2pdr guns, adding and inch to deck armour, additional generator capacity and extra ammunition stores.
She differed from all other RN monitors by having a circular armoured barbette instead of 12 armour plates arranged in a dodecagonal shape.
Both ships served both as monitors and floating flak batteries during the war, mainly in the Med' but later off of the Normandy beaches - both duties which they excelled at.