D5
The Navy is looking at the Trident in light of “all of those new technologies that we need to go think about on how we’re going to take what we have today, how we’re going to modernize it and how we’re going to get it to last the entire life of the Columbia, which is we all know about 2084,” Vice Admiral Johnny Wolfe, head of the Navy’s Strategic Systems Program, told a Naval Submarine League conference.
This would be the second life extension upgrade to the Trident II, which began receiving its first life extension in 2017. “Wolfe said the original life extension effort has gone well, with five flight tests in the last year showing the missiles can still fly the tracks they’re supposed to,” according to USNI News. “In fact, three motors involved in a test that were about three decades old performed like new during the test, he said.”
The three-stage Trident II D5, which has a range of 4,600 miles and carries multiple nuclear warheads, replaced the older Poseidon submarine-launched ballistic missiles (SLBM) in the 1990s. But now the Trident faces the same problem as older weapons: no one makes parts for them anymore. The U.S. Air Force has faced immense problems finding parts for its F-22 fighter, which first flew in 1997. After F-22 production stopped in 2011, manufacturers closed production lines and stopped making components.
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https://www.forbes.com/sites/michaelpeck/2020/07/21/older-than-the-b-52-americas-trident-missile-may-fly-until-2084/#7a7e0f794de5
"Features
The Trident II SWS is deployed aboard Ohio-class submarines, each capable of carrying 20 D5 missiles. Under the provisions of the Polaris Sales Agreement, it is also carried aboard the United Kingdom's Vanguard-class submarines.
The Trident II D5 SLBM is a three-stage, solid-fuel, inertially-guided missile with a range of 4,000 nautical miles capable of carrying multiple W76-Mk4/Mk4A or W88-Mk5 reentry bodies. The missile is launched by the pressure of expanding gas within the launch tube. When the missile broaches the waterline, it enters the boost phase, expending its first, second, and third-stage rocket motors. Following third-stage motor separation, the missile deploys the reentry bodies.
The Trident II SWS, originally designed to have a service life of about 25 years, has proven itself as a highly accurate and reliable system. To address aging and obsolescence issues, the Trident II SWS' life was extended. Life-extended Trident II D5 missiles (D5LE) were introduced to the Fleet in early 2017. These D5LE missiles will serve throughout the remaining service life of the U.S. Ohio-class and UK Vanguard-class submarines and they will be initially carried aboard the U.S. Columbia-class and UK Dreadnought-class submarines.
Background
The SLBM has been an integral part of our Nation's strategic nuclear deterrent Triad. As the most survivable leg of the Triad, the SLBM provides the Commander, U.S. Strategic Command, the National Command Authority, and the President with assured second-strike capability. Starting in 1956 with the Polaris (A1) and evolving through five subsequent generations including Polaris (A2), Polaris (A3), Poseidon (C3) Trident I (C4) and today's force of Trident II (D5), each generation of the missile has increased in range, payload, and accuracy."
https://www.navy.mil/navydata/fact_display.asp?cid=2200&tid=1400&ct=2