The primary U.S. SLBM (Sea Launched Ballistic Missile) recently had its 135th successful test launch. The 58 ton, 14.2 meter (44 foot) long Trident II, has since 1989, had an unbroken string of the 135 successful test launches. The Trident had two failures during its 49 development test launches, but since then, it has been the most reliable SLBM to ever enter service. Each Trident II costs about $65 million, and entered service in 1990. Some of them are fired every year, to insure that the current configuration (of hardware and software) still works as it is supposed to, and to give the launch crews on the subs some experience with the real thing.
While failures are expected during development, later maintenance, modifications and upgrades are also expected to introduce conditions that can cause a failed launch. That simply hasn't happened, yet, with the Trident II. The Trident II needs some major upgrades. For example, the guidance system uses 1980s era electronics, and is becoming impossible to maintain. That's because many key components are not manufactured anymore, and supplies of these spares are running out. So the U.S. Navy is developing a new guidance system, using current components, and a design that makes it easier to substitute future, and more powerful, components for those that become obsolete.
Russia is developing a missile similar in design to the Trident II, and has had lots of problems. While the similar Russian Bulava is less reliable, it is using more modern components than the Trident II. But there is something wrong with the basic Bulava design, and the way it is put together. So far, half the 14 test launched have failed. The original Trident SLBM, the Trident I, had a failure rate of 13 percent while in development during the 1970s. The 48 ton, 18 meter (56 foot) long Bulava costs about the same as the Trident II. Russian leaders insist that the Bulava will eventually succeed. But insiders say that, if you use the same criteria for a successful Trident II launch, only two of the 14 Bulava tests was a success. While the overall (out of over 5,000 of them) failure rate for test launches of Russian rockets is eight percent, the Bulava uses a lot of new technology (for the Russians) and the development is being done by a workforce much depleted by the best people leaving for more lucrative jobs in the private sector. In contrast, test firings of older Russian ICBMs, built before the Cold War ended in 1991, have been much more successful than Bulava.
Currently, 12 of the 14 American Ohio class SSBN (ballistic missile carrying nuclear subs) carries the Trident II D2, and the other two will receive that missile the next time they are in for refit. The Trident II is expected to remain in service for the life of the Ohio class boats, which means another two decades of service.