Watch: What's on the new First Sea Lord's to-do list?

The procurement of new frigates which began under the incoming CDS will now fall to Admiral Sir Ben Key to progress.

Admiral Sir Ben Key will come into his new post as First Sea Lord just as warnings are sounded about fleet numbers from a former Navy chief.

Former First Sea Lord, Admiral Lord West, has raised concerns that the Royal Navy's fleet of frigates could fall short of the Government's promised minimum size and that replacements of ageing stock are not being delivered quickly enough.

Defence analyst Professor Michael Clarke agrees that the main challenge for Adm Key as he takes up his new post is to continue delivering the modernisation of the Royal Navy.

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He said: "The most important issue was the same one facing his predecessor, Tony Radakin, who's now stepped up to CDS (Chief of the Defence Staff), and that is to deliver the modernisation, the transformation that the Navy is committed to.

"All three Armed Forces have to transform themselves by 2030, joining up as an integrated force.

"The Navy has its own challenges with robotics and new ship designs, and the main challenge for Ben Key is to keep the continuity in driving forward that transformation.

"You have to stick with it day after day and sweat the detail. I suspect he will do that."

So, let's look at that detail.

There are two types of new frigates currently in production in Scotland and one still in design phase.

The Type 26 'City Class' are being designed as anti-submarine warfare (ASW) vessels, replacing eight of the Type 23s, protecting the UK's nuclear deterrent and the Queen Elizabeth class aircraft carriers.

Watch: Take a virtual tour of the future Type 26.

There's international interest in the UK-designed Type 26.

They are expected to be ready for delivery by the mid-2020s.

The Type 31e vessels are to replace five general-purpose warships which have served the Royal Navy since the start of the 1990s.

The 'Inspirational Class' are intended to be 'light' and cost no more than £250m each, carrying a main gun, surface to air missiles and a hangar to operate helicopters.

Production began on the first Type 31e in September and it is due to enter service in 2023.

All five vessels are expected to be operational by 2030.

In the interim, keeping the Type 23s running could prove challenging as 2030 is double the time they were planned for. 

Watch: Admiral Sir Ben Key - who is the new First Sea Lord?

The Type 32 design is rumoured to be an Unmanned Systems Mothership, providing replacement capabilities for the Sandown and Hunt class of minehunters due to retire shortly.

There is yet to be an order for the Type 32.

Commenting on the future of the Royal Navy, Professor Clarke said: "In this era of global Britain, should we achieve it, the Navy will be one of the hard power assets at the forefront of that.

"As far as the military is concerned the Navy is the most globalist of the three services and that was the thinking behind the carriers, having two of them should mean they have a fairly wide role."

BAE Systems computerised image of future Type 31e frigate CREDIT BAE SYSTEMS.jpg
A computer-generated image of a Type 31e frigate (Picture: BAE Systems).

Aggression from hostile states requires warships to deploy, for example, to the heavily disputed South China Sea.

This was a focus for CSG21 in the Indo-Pacific, unifying interoperability with allied forces and demonstrating capabilities.  

Early into CSG21's Indo-Pacific deployment HMS Diamond, a Type 45 Destroyer on the mission, had to return to Italy for repairs leaving only one of six Destroyers available, HMS Defender.

Meanwhile HMS Dauntless is due to be available for sea trials after a £160m engine upgrade.

But the scarcity of operational destroyers was highlighted in Defence Select Committee meetings at the time.

Infographic showing a Type 45 vessel and land assets with laser weapons (Picture: BAE Systems/Thales).

The strategic review states the "lethality of the surface fleet" will be increased by upgrading the air defence capability of the Type 45 Destroyers with the Common Anti-Air Modular Missile (CAMM) programme, often referred to as Sea Ceptor, into the destroyers' current Sea Viper weapon systems.

The review nodded to the possibility of a new Type 83 Destroyer being developed, although this looks more like the late 2030s. 

The question for Adm Key is whether plans are developing quickly enough to replace outgoing stock and meet modern threats while striking the right capability balance.