Retiring Trident

Retiring Trident
The records suggest that Margaret Thatcher’s 1979 decision to purchase
Trident I (C4) 102 did not make a decision between these options; a single
Trident I C4 SSBN could meet the Duff Group’s Options 2, 3a and 3b, but
two SSBNs at sea were required to meet the requirements of Option 1. 103
The 1982 decision to move to the more accurate Trident II D5 was driven
by commonality with the USN, but ensuring that a single SSBN could fulfil
Duff’s Option 1 targeting plan was described as “a valuable but incidental
advantage”. 104
What level of nuclear capability does the UK require?
For the purposes of this paper, unacceptable loss is the Duff Group’s Options
3a or 3b. These options were designed to be sufficient to deter the
Cold War Soviet Union, through an attack on the sources of Soviet power,
and the means of state control. Against today’s Russia, which lacks
the coercive power of the Soviet state, or against smaller or less developed
nuclear states – e.g., Pakistan or North Korea – the state’s power
structure is less survivable as the former Soviet Union, meaning that the
amount of damage representing unacceptable loss – when deterrence is
achieved – is likely to be smaller.
However, demonstrating how conservative the assumptions in this paper
are, we will continue to use the Duff Group’s Options 3a or 3b. That is,
deterrence will be achieved if a potential adversary does not have a high
level of confidence that it can stop the UK destroying at least ten of its
cities, or that it can stop the UK delivering 30 warheads to target.
Value for Money (VfM)
If two competing nuclear systems can meet this requirement, and in so
doing, that they can inflict unacceptable loss on a potential adversary,
then public sector VfM considerations dictate that the less expensive system
is adopted.
Trident II Capability
Trident II’s Multiple Independently-targeted Re-entry Vehicle (MIRV) capability
was designed in the 1980s to provide a highly survivable first
strike capability against very heavily hardened targets – e.g. Intercontinental
Ballistic Missile (ICBM) silos 105 – from SSBNs for the first time. 106
Prior to this, the inaccuracies of SLBM warheads and their comparatively
small yield meant that counterforce 107 targeting could only be delivered
by USAF ICBMs with larger warheads (335kt 108 – 9Mt 109 ) to create the
necessary overpressure to guarantee the destruction of the most hardened
targets. The challenge was to meet similar performance criteria to
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