The 6,800-ton Veinticinco de Mayo and Almirante Braun design was derived from the Italian Trento class. The ships were smaller than the original, and carried significantly less armour. They had a clean and simple design, with a length-width ratio of almost 10:1. Three twin turrets were mounted with an elevation of 46 degrees for firing.
The main 190 mm (7.5 inch) guns were designed especially for this class for greater stability (the Trento-class carried 203 mm (8 inch) guns). This could have been a quite powerful gun, but no documents about its characteristics are available in Italian or Argentine archives. The guns had single mounts to simplify construction, and could fire a 90 kg (200 lb) shell up to 23 km (30,000 yards). Despite this reduction in size and weight, they were still too heavy, so the number of turrets were reduced from four to three.
The secondary armament was also a new design, similar to standard 100–102 mm guns of the time. It consisted of twelve 102 mm (4 inch) DP guns, firing a 13.5 kg (30 lb) shell, all in twin mounts. This was an unusual arrangement for Italian heavy cruisers, which generally carried only four to eight of these weapons. However to counter the additional weight, gun shields were removed, which adversely affected their operability in bad weather conditions.
Unusually, the torpedo tubes were in fixed mounts amidships firing abeam, which caused problems in aiming effectively.
Neither vessel played a role in WWII or any other military conflict. Both were decommissioned in 1961.