'Seemöwe' (i) was a German mission planned and prepared by the Abteilung II of the Abwehr military intelligence department and Hauptmann Dr Theodor von Hippel’s Lehr-Regiment 'Brandenburg' zbV 800 to infiltrate German agents and saboteurs in the UK in preparation for 'Seelöwe' (September 1940).

'Seemöwe' (i) was schemed in the context of the Abwehr's remit to gather intelligence about the defences of the UK in preparation for 'Seelöwe'. The mission was aborted during the sea crossing to Ireland, but was launched despite the fact that the head of the Abwehr, Admiral Wilhelm Canaris, had previously ordered that the Abwehr's regional stations were not to attempt infiltration operations to the UK via Éire (Irish Free State) as a result of the amateurish planning and total failure of 'Hummer I' in July 1940.

Despite Canaris’s instructions, 'Seemöwe' (i) was ordered by the German army high command in northern France and Belgium via the Lehr-Regiment 'Brandenburg'. Christian Nissen (otherwise Hein Mück) had already taken part in 'Hummer I', and his orders were to use the vessel Anni Braz-Bihen for the delivery of a non-commissioned officer from the Lehr-Regiment 'Brandenburg', Helmut Clissmann, and one Abwehr Abteilung I radio operator to the south coast of Éire to carry out their mission.

Clissmann had a two-part mission. Firstly, he and the radio operator were to be landed by boat in the southern region of Éire, establish contact with the Irish Republican Army, and secure IRA assistance to get to the UK. Secondly, after arriving in the UK, Clissmann was to locate persons who would be able to guide a Lehr-Regiment 'Brandenburg' invasion detachment to the area of Dover. If travelling to the UK proved impossible, Clissmann was to enlist the help of the IRA in searching within Ireland for the required guides.

If they had to remain in Ireland, the two agents were to make contact with Hauptmann Hermann Görtz, the German liaison officer with the IRA, through the German legation in Dublin. During the crossing from France things went wrong (the boat’s bilge pump failed, the Danish mechanic was rendered unconscious by an accident, and the vessel was buffeted by a heavy storm for three days), and Nissen turned back to Brittany.

The IRA was not forewarned of the operation.