[48] On 23 November, The Times reported that Diamond was being forced to abandon her deployment and return to Portsmouth early due to mechanical issues, which was later confirmed by the Ministry of Defence.

[49][50] On 10 April 2021, Diamond left Portsmouth to conduct a 41-gun salute after the death of His Royal Highness Prince Philip, the Duke of Edinburgh.

[54] In mid-October 2021, after rejoining the strike group, the destroyer again experienced "technical issues", this time reportedly not related to her propulsion system and a decision was made to dock in Singapore to have them addressed.

[55] In September 2023, Diamond, with a Wildcat HMA2 helicopter, again escorted Queen Elizabeth for her "Operation Firedrake" deployment in northern European waters.

[60] The Houthis, backed by Iran, intensified their attacks in the area, targeting both commercial vessels and military ships, including those from the United Kingdom.

[61] In the aftermath of the shoot down and a spate of attacks by Houthi militia on civilian vessels Diamond was assigned to join the international task force protecting ships that travel through the Red Sea.

[67] After resupply HMS Diamond then returned to the Red Sea, including providing escort to the ships of Littoral Response Group South as they deployed to the Indian Ocean.

On 24 April 2024, Diamond defended the American container ship MV Maersk Yorktown and shot down a Houthi anti-ship ballistic missile.

This was the first ballistic missile kill for the Sea Viper air defence system and the first Royal Navy missile-to-missile interception in combat since the Gulf War.

[71] Diamond is primarily designed for anti-air warfare, able to defend against targets such as fighter aircraft, drones, and highly maneuverable sea-skimming anti-ship missiles travelling at supersonic speeds.

[72] The ship's SAMPSON active electronically scanned array multi-function radar system allows the Diamond to track threats from over 250 miles away, and to guide friendly missiles.

[73] MBDA describes Aster as a "hit-to-kill" anti-missile missile capable of intercepting all types of high-performance air threats at a maximum range of 120 km.

[75] The Aster missile is autonomously guided and equipped with an active RF seeker enabling it to cope with "saturated attacks" thanks to a "multiple engagement capability" and a "high rate of fire".