TRIDENT has been “blighted” by problems with navigation for years, according to new reports.

Documents from the US Department of Defense show officials have had to throw more than £1.4 billion at repairing faults and modernising the guidance system.

The documents came to light the week after Theresa May was accused of covering up a botched trial that saw a Trident missile veer off course and head towards the US before ditching into the sea.

Although no nuclear warheads were involved in the test, it happened in June last year, a politically-charged time when MPs were voting on committing billions to the renewal of Trident.

However, reports obtained by The Sunday Times show the US-made Trident II D5 missile has had difficulties with its gyro guidance system for some time.

Reportedly, the faults can be linked to a chemical reaction caused by ageing. Trident II was first deployed 27 years ago. The newspaper also claims a second Trident missile fired by the US Navy may have failed in 2011 and was also covered up, according to a source close to the US military.

The cause of the failure is not known, but an extra £215 million was diverted to fund unexpected work on the guidance system that year.

In a statement yesterday the MoD said: “We have absolute confidence in our independent nuclear deterrent.”

Earlier in the week, the Trident whistleblower William McNeilly told Russian government-funded news channel RT that he had witnessed four failures of the Trident weapons system. “I warned about this exact event over a year before it happened. I was in the Missile Control Center during the end of patrol tests in early 2015 and I witnessed with my own eyes the Trident system fail its simulated missile launch tests,” the sailor said.

McNeilly published an 18-page dossier of Trident’s failings in 2015, a year before the dodgy test that saw a missile head towards the US. In that he alleged there were 30 flaws on the submarines that carry Britain’s nuclear warheads and warned that Trident was “a disaster waiting to happen”.

The former Able Seaman, who was dishonourably discharged, said he had seen “three WP 186 Missile Compensating Tests” fail. He also says a “Battle Readiness Test (BRT) was not even attempted due to seawater in the hydraulic system”.

McNeilly wrote in that original dossier of potentially catastrophic failures that took place during a series of end-of-patrol “shakedown” tests, designed to see whether the weapons system “could have performed a successful launch”.

McNeilly says the routine tests are vital to determining “if we really were providing the UK’s strategic nuclear deterrent”. The test McNeilly witnessed was “carried out three times and it failed, three times”.

He added: “Basically the test showed the missile compensation system wouldn’t have compensated for the changes in weight of the submarine during missile launches. Which means the missiles would’ve been launched on an unstable platform, if they decided to launch.”