The Four Days' Battle, also known as the Four Days' Fight in some English sources and as Vierdaagse Zeeslag in Dutch, was a naval battle of the Second Anglo-Dutch War. Fought from 1 June to 4 June 1666 in the Julian or Old Style calendar that was then used in England, in the southern North Sea, it began off the Flemish coast and ended near the English coast. It remains one of the longest naval engagements in history. Dutch accounts referred to its dates as 11 June to 14 June 1666 by using the New Style calendar.
The Dutch inflicted significant damage on the English fleet, which lost ten ships in total, with over 1,000 men killed, including two vice-admirals, Sir Christopher Myngs and Sir William Berkeley, and almost 2,000 English were taken prisoner including a third vice-admiral, George Ayscue. Dutch losses were four ships destroyed by fire and over 1,550 men killed, including Lieutenant Admiral Cornelis Evertsen, Vice Admiral Abraham van der Hulst and Rear Admiral Frederik Stachouwer.