'Acid Drop' was a British special forces raid by elements of Lieutenant Colonel W. S. S. Sanguinetti’s No. 5 Commando on Hardelot, Neufchâtel-Hardelot and Merlimont on the north coast of German-occupied France (30/31 August 1941).

The first operation by No. 5 Commando after its formation in June 1940, this undertaking comprised a pair of simultaneous operations each carried out by a party of one officer and 14 men. The operation’s objectives were a reconnaissance of the beaches at Neufchâtel-Hardelot and Merlimont, and if possible the capture of German soldiers for interrogation. 'Acid Drop' was a hit-and-run raid with only 30 minutes ashore, but in the event neither party encountered any German opposition. Even so, useful lessons were learned and digested to the benefit of later operation