: The problem with that is... We had no need of such a capability.
: What an SSBN needs is a method of knowing it's position *without*
: having to surface, or preferably even coming close to the surface. We
: already had that capability with SINS, SINS/ESGM, and with ESGN.
: From the point of view of an SSBN, GPS is 'nice-to-have', not 'must
: have'.

I'm not certain I quite agree with that. The USN definitely needed
such a capability. For starters, SSBNs launch from relatively close to
the surface, and in launching advertise themselves very well, and are not
supposed to be anywhere near an enemy when they do. Thus, coming close to
or at the surface is not such a liability. This is particularly true if
you are going to be using satcomms for any purpose - verification, mission
update, etc.
Secondly, the USN wanted to be able to use SSBN launched missiles
in counterfire, not a a countervalue, role. You can nuke a city without too
much accuracy, but if you want to plink hardened silos and buried targets
accuracy becomes much more important. This is particularly true if you want
to move to using MIRVs against silo fields, etc. In addition, during that
time the USN was greatly improving its modeling databases and incorporating
this knowledge into missile guidance (for example, more precise gravitational
maps, etc.). To fully utilize such data and calculate its effects over the
course of the launch it helped to have a much greater accuracy in launch
locations and, eventually, with onboard GPS updating aboard the missile.
A lot changed in the intervening years, but the USN was clearly
looking at increasing submarine ballistic missile accuracies by orders of
magnitude to allow new missions and employment models. If the USN wanted
to improve it capabilities, it needed GPS or some suitable replacement.
INS is great, and it has improved as well, but it was not expected to be
able to match the accuracy of the GPS system or allow the kind of precision
firing that the USN wanted. (There are continuing arguments over just how
much accuracy is really efficient/needed - but the military back then was
clearly of the opinion there could not be too much of it).

regards,
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