'Springboard' was a British unrealised plan for the occupation of the Madeira islands, a Portuguese possession in the Atlantic, by invitation (spring 1941).
The plan was the partner of 'Puma' (i) and 'Thruster' (i) for the occupation and/or capture of all the Portuguese and Spanish island possessions in the Atlantic, but there were great difficulties in the fact that the total British amphibious capability of the period was sufficient for only about one brigade group.
The plan was designed as a means of projecting British anti-submarine capability toward the central Atlantic, and thus of denying the Germans the ability to base U-boats and maritime reconnaissance aircraft in the islands, at a time when it was expected that 'Felix-Heinrich' against Spain and Gibraltar would be launched as soon as Germany had dealt with the USSR in 'Barbarossa' during the late autumn of 1941. As it was, 'Barbarossa' was delayed first by 'Unternehmen 25' and 'Marita', and then the determination of the Soviet resistance, and Hitler never really had the opportunity for 'Felix-Heinrich'.
On the British side 'Springboard' was eventually built into the overall 'Pilgrim' plan.