The US has been quietly amassing firepower in the Pacific during a lull in tensions with North Korea, but recent developments on an under-the-radar nuclear weapon suggest preparation for a potential tactical nuclear strike.

The US recently sent B-2 stealth bombers to Guam, where they joined B-1 and B-52s, the other bombers in the US’s fleet.

While the B-2 and B-52 are known as the air leg of the US’s nuclear triad, as they carry nuclear-capable air-launched cruise missiles, a smaller nuclear weapon that has undergone some upgrades may lend itself to a strike on North Korea.

The B-61, a tactical nuclear gravity bomb that the B-2 can carry 16 of, has been modified in recent years to increase its accuracy and ability to hit underground targets, though that version has not yet been deployed.