This was a German plan to infiltrate agents and saboteurs into the UK from German-occupied Norway and northern France (July 1940/26 April 1942).
The plan was begun before the postponement of ‘Seelöwe’ but maintained even after what was in effect the cancellation of this plan for an invasion of England.
During Germany’s ‘Sichelschnitt’ defeat of the Low Countries and France, the Abwehr (German intelligence service) had been entrusted with the task of locating data, both current and accurate, on the UK’s defences and continued war-making capability. On 22 June, the day on which the Franco-German armistice was signed and three days before it came into effect, the Abwehr’s Abteilung II, which was responsible for sabotage and subversion, switched the focus of its activities to the UK, and at about this time the Oberkommando der Wehrmacht issued planning directives asking Abwehr’s Abteilung I (espionage) and Abteilung II for information on the UK’s defences, data on the feasibility of a German invasion of Ireland, and data on the creation and subsequent insertion of a ‘fifth column’ into the UK for sabotage and to pave the way for a German invasion.
One of the results of this request was ‘Hummer’, and this involved the despatch of missions to the UK by several means, most commonly by sea. ‘Hummer’ should be seen in the context of ‘Seelöwe’, which in turn involved ‘Grün’ (iv). Before ‘Seelöwe’ was postponed, the Abwehr inserted almost 20 agents into the UK and Ireland between the summer and early autumn of 1940, and of these 19 surrendered or were captured, and one committed suicide.
'Hummer I Nord' of 30 September 1940 involved the delivery of agents in the area of Banff in Scotland from southern Norway by sea and air.
'Hummer III Nord' of April 1941 involved the delivery of agents into the north of England with orders to undertake sabotage operations against the British aircraft industry, factories making military equipment, and railway communications.
'Hummer V Nord' of 26 April 1942 involved the delivery of agents onto parts of the English coast with instructions to attempt the destabilisation of these areas by the sabotage of coastal installations, but the sabotage team was arrested immediately after it had come ashore.