Fetching details from the dictionary...
torpedo
(sea) mine; underwater mine
「水雷」 has another reading with different meanings.
thunder accompanied by rain
敵艦てきかんに水雷すいらいを発射はっしゃしました。
A torpedo was launched at the enemy ship.
水雷すいらいが命中めいちゅうして爆発ばくはつした。
The torpedo hit and exploded.