'Caddie' was the US geographical rather than operational codename for Mille atoll (later codenamed 'Lockman') in the Ratak chain of the the southern part of the Marshall islands group in the central Pacific (1941/45).

Mille lies 65 miles (105 km) to the north-west of Majuro atoll, 165 miles (265 km) to the north-north-west of Wotje atoll and 145 miles (235 km) due west of Jaluit atoll. Like the other atolls of the Marshall islands group, Mille was taken from the Germans in World War I by the Japanese, who then received a post-war League of Nations mandate to administer the group.

Mille atoll comprises 92 islands and islets with a total land area of 5.8 sq miles (14.9 km²), making it the second largest of the Marshall islands group after Kwajalein. The atoll encloses a lagoon considerably smaller than that of Kwajalein, with an area of 293 sq miles (759 km²). The atoll is separated by the Klee Passage from the Knox atoll, which is considerably smaller. Mille atoll is about 20 miles (32 km) long on its west-north-west/south-east axis and about 10 miles (16 km) wide, and its islands and islets are distributed along most of the atoll’s rim, whose eastern side is open.

By the outbreak of the Pacific War, Mille sported a radio direction-finding beacon and a weather station, and was then developed as a major base with a garrison that peaked at 2,045 naval and 2,237 army personnel, as well as a significant number of civilians. In 1942 a seaplane base was developed, and in the period between late 1942 and late 1943 the Japanese also constructed a land airfield with an X-shaped arrangement of three runways, measuring 4,750, 4,550 and 4,400 ft (1450, 1385 and 1340 m) in length, and many support buildings including a radar station. This was the only Japanese airfield within fighter range of the Ellice islands group, and fighters from Mille escorted some of the Japanese bombers which attacked targets in the Ellice islands group. The island’s shore was fortified with coast-defence and anti-aircraft artillery.

The fate of Mille atoll in the period after the US forces had taken their main objectives in the Marshall islands group is essentially similar to those of Jaluit ('Deadwood'), Wotje ('Creosote') and Maloelap ('Corsial'), inasmuch as the atoll was bypassed and left to 'wither on the vine' without direct assault from the sea. Thereafter small quantities of supplies did occasionally reach the isolated garrison by submarine, but at the cost of I-32 and I-184.

Even so, between the middle of 1943 and August 1945, Mille was bombed by carrierborne warplanes and shelled by warships on several occasions. The attacks increased in both severity and frequency after the US forces had taken Majuro and Kwajalein. Of the 5,100-man Japanese garrison (2,600 naval and 2,500 army personnel), 1,600 died of disease or starvation, and another 900 were killed or died of their wounds during or after US air attacks, so fewer than half survived to the end of the war.

On 22 August 1945 the Japanese garrison commander surrendered his forces on board the US destroyer escort Levy.