subsonic combat

例句：

1. 1. The aircraft flew at a subsonic speed.
   飞机以亚音速飞行。
2. 2. The sound of the engine was barely above the noise level.
   发动机的声音几乎低于噪音水平。
3. 3. The rocket reached hypersonic speeds before it exploded.
   火箭在爆炸前达到了超音速。