South Atlantic UAP — Royal Navy HMS Sheffield Area Report

In March 1977, Royal Navy personnel operating in the South Atlantic Ocean documented an encounter with an unidentified aerial object that was observed approaching at speed, hovering over the water, and then apparently descending into the ocean before re-emerging. The object then departed at high speed. The encounter was documented in a classified Royal Navy report forwarded to the UK Defence Intelligence Staff (DI55). The report was classified SECRET. Under the UK's 30-year declassification rule, the document became eligible for release in 2007. Portions were released through the UK National Archives at Kew. The South Atlantic encounter is part of a documented pattern of UK military UAP reports from the 1970s that also includes the 1980 Rendlesham Forest incident and the 1990 Calvine photographs. The Royal Navy's willingness to formally document transmedium behavior — the object entering and exiting the ocean — is notable as it parallels US Navy AARO's formal acknowledgment of transmedium UAP in 2021. The released UK MoD files from this period are available in the DEFE 31 series at the National Archives.