'Musketeer' was the US cover designation within the 'Reno V' scheme in which the plans for the reconquest of the Japanese-held Philippine islands and Netherlands East Indies, initially schemed as 'Princeton', were studied and initially prepared before being translated into the definitive 'Montclair' and 'Oboe' plans (1943/44).

Before the launch of the 'Mike' operations for the US forces to thrust into the northern parts of the Philippine islands group, the basic 'Musketeer' plan was refined as 'Musketeer II' early in 1944 and then fully defined as 'Musketeer III' on 26 September 1944 and approved on 13 October as the final version of 'Musketeer II' for landings on Leyte, Luzon and Mindanao islands in the 'King', 'Mike' and 'Victor' series of operations respectively.

The plan envisaged the US seizure of a significant foothold on southern part of Mindoro island off the south-west coast of Luzon island on 15 December. This move was deemed necessary as poor weather conditions continued to hamper the construction and development of airfields and the associated air operations on Leyte island, taken in 'King II', a fact which would hinder air support of the 'Mike I' landing on Luzon, initially scheduled for 20 December. Mindoro island would also provide airfields closer to the main objective. The lightly defended main islands in the Visayan islands (Panay, Negros, Masbate, Cebu and Bohol) would be secured concurrently.

A total of two army headquarters, four corps (including one Australian) and 14 divisions (including two Australian) were envisaged for this operation, although it was not necessary to commit all of these formations in the operation that then followed as 'Love III' and the 'Victor' undertakings.