“Unprecedented”

Here we provide some more details of HMS Prince of Wales’ recent mechanical breakdown, plans for repairs and how HMS Queen Elizabeth’s programme is being altered in response.

Broken coupling

The reason HMS Prince of Wales could not begin her planned deployment is that an external SKF coupling that connects the outer propellor shaft to the drive shaft from the propulsion motors failed. This is a rare event and a situation described by the First Sea Lord as “unprecedented” as few marine engineers can remember an instance of this happening. Random unpredictable failures are uncommon but can still occur even if equipment is well designed, maintained and operated.

However, unconfirmed sources suggest HMS Prince of Wales was already experiencing some significant problems with her starboard motors and under pressure to sail, required special permission to leave on Saturday with a known defect. Her sailing had already been delayed by 24 hours and she put to sea with civilian staff from the original equipment manufacturer (GE Power Conversion) onboard, presumably confident the motor could be repaired while underway. Whether the coupling failure was related to the motor issues is unclear. She appears to have sailed using only the port shaft and her propellors did not strike the sea bed as has been rumoured. Press reports that the breakdown was caused because RN engineers “forgot to grease the shaft” are contemptible nonsense. (The external bearings are sea water-lubricated for starters).

Repair in Rosyth

The ship will return to Portsmouth in the next couple of days to offload some stores and a temporary fix will have to be applied to lock the faulty shaft to prevent damage while she on her way to dry dock. Tidal windows that allow the carriers to pass under the Forth Bridges and over the dock sill are only available every few weeks but Rosyth will be the destination. Despite rumours she might use dry docks in Amsterdam to save time, Rosyth was always by far the most likely option for the repair. Babcock has a contract to keep the facility ready for unplanned dry docking of the carriers at their secure site with personnel already experienced working on the ships. This will not be a quick fix and expect PWLS be out of action for some time. It is possible her 5-yearly Lloyds Naval Ship Rules hull inspection which was due next year anyway will be brought forward and combined with the repair work, allowing more availability for her in future.

Building large aircraft carriers was the right decision in almost every respect but comes with the downside of requiring bigger infrastructure. This incident highlights the unfortunate fact that there is no dry dock large enough to accommodate these vessels in their home port of Portsmouth. To construct such a facility in Pompey has been estimated to cost around £500M, funding the RN simply does not have. Rosyth with all its constraints remains the only viable option for the foreseeable future.

Photo: The port tail shaft being fitted to HMS Queen Elizabeth during her construction in dry dock at Rosyth in 2014. In these large ships, the length of the shafts requires them to be made of sections that have to be connected together with couplings. Note the rudder is offset inboard to allow the shaft to be slid in (or out) of the stern tube (Photo: Aircraft Carrier Alliance).

Sister act

Demonstrating the advantages of having two aircraft carriers and subject to final ministerial approval, HMS Queen Elizabeth will take over some, but not all, aspects of her sister’s programme. QNLZ was due to commence a 4-month deployment to the Baltic and Mediterranean with embarked F-35 jets. Instead, she will sail next week for the east coast of the US with her escorts HMS Defender, Diamond and Kent. She will perform some of the defence engagement tasks that were planned for PWLS, in particular hosting the Atlantic Future Forum in New York (28-29 September). HMS Richmond and RFA Tideforce were originally scheduled to accompany PWLS and will likely also continue on the deployment as planned.

QNLZ has not been fitted with all the kit required for the flight testing that was going to have taken place on PWLS and with limited time available, developmental flying will have to be severely curtailed or cancelled. Details of the programme are obviously still evolving but she is likely to re-cross the Atlantic to resume operational tasking in the Mediterranean, leaving some of the escorts behind to continue the diplomatic visits.

That’s life in a blue suit

As ever, the RN is able to respond flexibly to unforeseen events but people behind the scenes are having to put in lots of extra work to rearrange plans at short notice. Spare a thought for HMS Prince of Wales ship’s company who will be threaders, while those serving in her sister ship can instead look forward to the ship making her second visit to New York. This is a very unfortunate and regrettable way for the RN to begin its busy Autumn programme and the negative headlines, media pile-on and misinformed speculation has been rife. At least the video updates presented by Rear Admiral Moorhouse have shown the RN trying to be more proactive on the communications front.

Looking at events from a wider perspective, the RN is fortunate to have two active carriers and was about to launch simultaneous deployments. Better to break down off the Isle of Wight than on an operational or combat deployment far from home. The temporary loss of one ship can be mitigated by the availability of the other to some extent, although at the cost of some presence in the European theatre. Apart from the PR and repetitional damage, further delay in F-35 SRVL developmental flying is perhaps the biggest single cause for concern resulting from the breakdown.