March 26, 2024:
Back in the early 1980s American warships began using VLS (Vertical Launch System) cells to carry the many different missiles ships used for attacking other ships, defeating air attacks, and bombarding land targets. Since 1982, over 11,000 VLS cells have been installed in nearly 200 American and foreign warships. The most common VLS user is the American Burke class destroyer, with 90 VLS cells.
The first ships to get VLS also received a strikedown crane so the cells could be reloaded at sea. By 1990 new models of missiles became too heavy for the strikedown crane and it wasn't practical to install a larger and more powerful crane. Moreover, there were few opportunities for reloading the missile cells at sea anyway and the strikedown crane was omitted in new ships. This provides space for 3-6 more missile cells. Having to go to a port to reload VLS cells takes a ship away for several weeks or more from where it was needed.
After 2010, it became obvious that navy missiles capable of intercepting ballistic missiles were now more essential because Iranian and North Korean anti-ship ballistic missiles became a growing threat. This meant ships had to fire more missiles for missile defense as well as other tasks like anti-aircraft, anti-ship, anti-submarine, and land bombardment. It became increasingly likely that a ship would run out of some types of missiles.
That meant ships had to get replacement missiles for their empty VLS cells. The problem was that most of the missiles were too heavy and unwieldy to be loaded while the ship was at sea. This eventually led to TRAM, or Transportable Re-Arming Mechanism. TRAM works because of its articulated crane that can keep a replacement missile canister stable enough, even with winds up to 50 kilometers an hour and waves up to 3.2 meters high. TRAM has worked in tests but has not yet been tested extensively at sea. That may change in 2024 as a series of at-sea tests for TRAM will be conducted and, if successful, TRAM will be installed on some ships for sustained use at sea.