noun
barrage balloon
A large tethered balloon used as a defense against low-flying aircraft by supporting a network of cables.
第二次世界大戦中、ロンドン上空には多くの阻塞気球が浮かんでいた。
During World War II, many barrage balloons floated over London.
Compound of 阻塞 (そさい, 'obstruction') and 気球 (ききゅう, 'balloon'). The exact historical derivation is uncertain, but the term is a direct calque of the English 'barrage balloon'.