'Totter' was the British system whereby personnel of Air Commodore Finlay Crerar’s Royal Observer Corps fired 'Snowflake' illuminating rocket flares from the ground to indicate the location of V-1 flying bombs for interception by RAF fighters (1944/May 1945).

The Defence Committee had expressed doubt as to whether or not the Royal Observer Corps could deal adequately with the threat of V-1 flying bombs, but Crerar assured the committee that his personnel possessed the right combination of alertness and flexibility to undertake the task, and Crerar was then instructed to oversee the creation and implementation of the 'Totter' plan for handling the new threat. Observers on the south coast at the Dymchurch post identified the very first of these weapons and within seconds of their warning report the anti-aircraft defences were in action.

This new 'weapon' gave the ROC much additional work both at posts and operations rooms and, to increase the speed with with interceptions could be effected, RAF controllers eventually relocated with their radio equipment to the two closest ROC operations rooms at Horsham in West Sussex and Maidstone in Kent, and vectored fighters direct from the ROC’s plotting tables.