'Brush' was the US geographical rather than operational codename for Palmyra atoll (1941/45).
The atoll is small and part of the Line islands group of the central Pacific, lying some 995 miles (1600 km) to the south-south-west of Pearl Harbor in the Hawaiian islands group. The atoll comprises more than small islands disposed in a horseshoe shape 6 miles (9.6 km) long and 2 miles (3.2 km) wide, with the open end to the west. This horseshoe of islets encloses a shallow lagoon, and none of the islets is more than 7 ft (2.1 m) above high water. All of the islets are covered with dense scrub and coconut palms. The group receives more than 150 in (380 cm) of rain per year and the temperatures hover between 80° and 90° F (27° and 32° C) right through the year. With an area of 4.6 sq miles (12 km˛), the atoll was privately owned in 1941, though under naval administration since 1934, and had 32 civilian inhabitants all evacuated before the outbreak of war.
Palmyra was ideally located to be part of the 'air bridge' from the west coast of the USA to eastern Australia and the Philippine islands group, and boasted an airstrip by the time war broke out. This was located on Cooper and Menge islands on the northern side of the atoll, which were joined with material dredged from the lagoon. The first runway was 5,400 ft (1645 m) long, to which 3,700 ft (1130 m) were later added. The island was held and defended by 158 men of the 1st Marine Defense Battalion with four 5-in (127-mm) coast defence guns and four 3-in (76.2-mm) anti-aircraft guns.