The twin 4.5-inch turret was replaced by a single OTO Melara 76 mm gun and two quadruple mounts for Harpoon anti-ship missiles were fitted abaft of the funnel.

The Mk 10 Limbo ASW mortar was replaced by a pair of triple Mk 32 torpedo launchers, one mount on each side of the hangar, and its mount plated over so the flight deck could be increased to allow the ship to carry the larger Westland Lynx helicopter in lieu of the Wasp carried earlier.

Most importantly an automated combat management system, SEWACO V, was fitted to aid the ship's captain in decision making.

Pictures released in March 2011 show that modifications were made to KRI Oswald Siahaan with 4 SS-26 Yakhont VLS cells located in the quarterdeck beside the helicopter hangar.

Between 2003 and 2008, all vessels of the Ahmad Yani class had their existing steam turbine engines replaced with diesel propulsion.