How does the UK military defend?

UK Defence posture - how the military would response

Unlike International Terrorism, (albeit potentially for Cyber Attacks) the UK would actively respond to any aggresor launching a strike either on itself (using conventional or nuclear weapons) or on a NATO ally under Article 5 of the NATO agreement. [1]

Whilst the UK military is much smaller than it was during the Cold War, it still aims to pack-a-punch. The UK holds 225 nuclear weapons and these could be used by the Prime Minister to launch a retaliatory strike should s/he wish. There are a lot of details about this which are still kept under wraps, but below we discuss some of what is known.

TRIDENT

The UK's 225 nuclear weapons are based on the US Trident missile which is launched from one of 4 SSBN (Ballistic missile carrying) submarines. [2] Currently these are the Vanguard class submarines but will be replaced by the Dreadnought class from the 2030's.

According to [3] British submarine commanders are (unlike their US counterparts) able to launch their nuclear weapons without authorisation from land based command. The logic behind this is that were UK command taken out, then they are able to launch a retaliatory strike. One of a new Prime Ministers first task (on day 1) is to write 4 letters [4] (known as the letters of "last resort") to these commanders so that in the event the UK command structure is destroyed, they have written actions to take in that event. In the event that communication is lost, the commander would need to make a number of checks before launching the weapons including not hearing BBC Radio 4 broadcast (!!), communications with the mainland lost for 4 hours or there was definite evidence of a nuclear attack against the UK.

For a thorough and fascinating explanation of the UK chain of command and how the process would work - I recommend reading link [5] written by a former Submarine commander and Admiral in the UK navy (in particular some interesting thoughts in the comments). In it explains that the PINDAR (see Nuclear bunkers) bunker under the MOD building would be the key location from which the PM would communicate with the MoD. "The message is authenticated by the PM and encoded, and from the moment it leaves the PM’s hand it is handled at all stages by two nuclear-authenticated operators following strict protocols. The order is transmitted to the patrolling SSBN through several communication paths appropriate to the crisis; at least one of these can survive even a devastating nuclear attack upon the UK." Firing the missiles has to be an absolute last resort and "the PM would be briefed that it is better to issue a last safe moment launch order than to issue one in advance and trust to a further message being transmitted and received if the circumstances or the PM’s mind were to change.".

However in February 2024 it was reported by the BBC [12] that a Trident missile test from HMS Vanguard had failed although "it was event specific and there are no implications for the reliability of the wider Trident missile systems" according to the BBC article! And in September 2024 it was reported that a new Russian RS-28 Sarmat ICBM equally failed [13]. Clearly maintenance and development of the longer range missiles is crucial and a fascinating question as to how many of these (praise God) rarely used weapons would ever get off the ground!

NATO

NATO would form the backbone of any nuclear war situation as any attack on the alliance would evoke the NATO doctrine that everyone had been attacked (Article 5). NATO has the NRF (Nato Response Force) which will comprises over 300,000 troops [7] able to defend Europe and a "NATO’s Very High Readiness Joint Task Force (VJTF) was created after Russia’s illegal annexation of Crimea in 2014 and deployed for the first time for the collective defence of the Alliance after Russia’s full-fledged invasion of Ukraine in 2022." [8] The UK will lead the VJTF during 2024.

Previous leaders

2024 - United Kingdom
2023 - Germany
2022 - France

More precise info about the leadership can be found on the UK Army website [9] but the "UK’s total contribution is 4,200 troops drawn from 55 units across the Field Army.".

British Army of the Rhine

Were the Soviets to have invaded, Western Europe would have been at risk. The only routes to invade the UK directly are by sea and as such, only the Nazi's during World War 2 were ever close enough. Had the Soviets taken France however the risk was quite real. This explains why the British Army were deployed to Germany (as opposed to staying in the UK) because that was the Front line. Since the Cold War, the Front line has moved further east including the Baltic States, Poland and Romania/Moldova.

We discuss the threat of war with Russia on the Ukraine page

At the end of the Cold War, [14] the UK had 3 Armoured divisions based in Germany and 1 Infantry division based in the UK.

1st Armoured Division (based in Verden)
2nd Infantry Division (based in the UK)
3rd Armoured Division (based in Soest)
4th Armoured Divison (based in Herford)

Comparing this list with the current list below the structure of the Army has clearly changed to more "light" and "specialist" focus rather than the heavy armour. However Ukraine has shown that were a war to break out with Russia then the UK would potentially need more tanks. However the way the battle has been fought shows that tanks aren't always the answer and sometimes modern "light" equipment is still able to be a formiddable force against them.

UK Army

Over the years how the army fights has changed dramatically. During WW2 "the basic tactical formation used by the majority of combatants was the division. It was a self-contained formation that possessed all the required forces for combat, which was supplemented by its own artillery, engineers, communications and supply units" [10]. In 1939 the UK had 33 divisions including 24 infantry. Interestingly, many divisions which fought were raised by the wider Empire not just purely UK mainland citizens.

Today's war fighting is orientated around brigades and the idea of divisions is more organisational and different brigades and regiments are pulled into the various required roles. According to [11] The United Kingdom is the only European power that retains its own heavy lift air transport capabilities... This means that unlike France or Germany, once a UK Brigade Combat Team is in the field, the UK has the capacity to sustain it indefinitely."

The UK army has 3 divisions:

1st Division (deployable) - contains "light" rapid response elements including the 16 Air Assault Brigade - the largest army brigade
3rd Division (deployable) - the "Iron division" - heavy equipment such as tanks
6th Division - a new "specialist" division including things like Cyber warfare

UK in Europe

The assumption was that the military would not just be focused on the nuclear theatre. During the Cold War, designated roads would be fully closed off to the public to enable British forces to deploy to mainland Europe, where, Soviet (codenamed Orange) forces would be presumably invading . This lead to a permanent deployment of the Army to Germany, which after the Strategic Defence and Security Review in 2010 lead to the full withdrawl by 2020.

However by November 2021 the Government planned a u-turn and sent equipment back to Germany to better assist should Russia ever attack a NATO country. [6]

What is interesting however, is that whilst Army resources will be based in Germany, combat forces won’t. In short Germany will store (and be used for NATO training) various Army resources (tanks etc) which would, in the event of a war take a good while to deploy to the mainland. Moving combat troops would be much quicker and simpler.

The UK leads the Enhanced Forward Presence (EFP) deployment in Estonia with 1000 troops deployed there with another 2500 " held at high readiness in the UK to reinforce Estonia and the wider Baltic at a time of crisis." [9]