HONG KONG — The tropical sky off Singapore was utterly dark when an oil tanker plowed into the side of the American destroyer John S. McCain before dawn on Monday — but the moonless night may have been only one of the reasons the tanker’s crew may have had trouble seeing a warship in their path.

Hard to see and hard to track electronically, naval vessels have long posed special perils to nighttime navigation. That has proved deadly this summer in crowded waters like those near Singapore and Tokyo, where another United States warship, the Fitzgerald, was struck by a cargo freighter under a waning crescent moon on June 17.

The issue has prompted growing alarm in the commercial shipping industry — which has started warning merchant vessels to be extra careful around warships — and in the United States Navy, which began pausing its worldwide operations this week for a day or two to allow time for safety reviews.

“There have been four this year for the U.S. Navy, and the Singapore Navy has experienced one or two” collisions with commercial ships, said Capt. Raymond Ambrose, the president of the Singapore Nautical Institute. “We need an attitude of defensive driving out at sea.”