'Felspar' was the US geographical rather than operational designation for Shemya island in the Aleutian islands group of the northern Pacific Ocean (June 1942/August 1945).

Shemya is the most easterly of the small Semichi group of islands within the Near Islands, and lies 137 miles (220 km) to the north-west of Kiska island and 35 miles (56 km) to the east-south-east of Attu island. With length of 4.3 miles (6.9 km) and maximum width of 2.75 miles (4.4 km) for an area of 5.9 sq miles (15.3 km²), Shemya is unusual among the Aleutian islands being generally level, but does possess rolling terrain and some high ground, peaking at 240 ft (73 m). Other than a few small ponds and patches of scrub, the island is featureless.

The island was uninhabited when 1,100 Japanese troops of the 303^rd Independent Infantry Battalion occupied it shortly after the Japanese 'Aq' seizure of Attu island in June 1942 as an outer defence for the latter. The Japanese remained in occupation for only a short time before withdrawing to Attu island in August before the US secured it as a staging base for their 'Landcrab' and 'Cottage' assaults on Attu and Kiska.

The US forces developed Shemya as a Boeing B-29 Superfortress four-engined heavy bomber base in June 1943, but in fact no aircraft larger than Consolidated B-24 Liberator four-engined bombers were located there during World War II.