Algarve was in a pleasant position that they were allowed 105,000 tons of capital ship construction that could be used to build battleships after 1930. These ships were to replace the last four of the Newport class 12" battleships. The unpleasant part of it was that they could only afford two. Designs were made for 35,000 ton ships that were to be improvements of the Jupiter Class. With the advent of the Wall Street crash and the following depression, funding was rescinded. This allowed further plans to be drawn up so that when the ships were finally laid down in early 1932 they were designed with the latest weaponry that was then available.
The ships ended up being 2,000 tons overweight, which when compared to some other designs, that was a very near miss. A new triple 15" turret and gun was designed and built along with a new dual purpose twin 4.5" gun system that was ready for installation from 1935 as the ships had been designed for it. The ships took just over 5 years each to build, the Mars being completed just in time to go to King George VI's Coronation review at Spithead. Compared to the other foreign ships that were at the review (Graf Spee and Ashigara) the Mars was a demonstration of power and grace.
Displacement: 37,000 tons standard, 45,400 tons full load.
Dimensions: 787 x 106 x 28 feet
Machinery: 4 shaft, geared turbines, 150,000shp
Speed: 28 knots
Endurance: 10,000 miles at 15 knots
Armour: 12" belt, 6" deck, 13/8/5" turrets
Armament:
9 x 15" (3x3)
20 x 4.5" (10x2)
50 x 40mm (25x2)
Aircraft:3
Crew: 2200