Doesn't start limit the entire use of nuclear warheads, meaning the IRBM's can't be nuclear?
No.
SALT was Strategic Arms Limitations Treaty.... in other words... stop making more, there are too many now.
START was Strategic Arms Reduction Treaty... in other words 10,000 nuclear warheads in ICBMs and SLBMs and Cruise missiles on Strategic Bombers is too many... reduce. START II got down to 6,000 warheads each and New START reduced that to just over 1,500 each but it only counts ICBMs, SLBMs, and Cruise missiles carried in long range bombers.
Intermediate range cruise missiles and intermediate range ballistic missiles is a separate category.
New START does not include tactical nukes either.
The loss of the INF treaty has created a serious gap, but I hope they don't bother fixing it... it counters the UK and France for Russia and China for the US not being in START.
The Russians can point their IRBM/IRCMs at US bases in Europe and the US can point its IRBMs and IRCMs at the Russian Far East from Japan and South Korea and Alaska, but that is not a serious problem for either really.
First it was 5.000km, was changed to 5.500km because the Pioneer-UTTH could reach that range.
Indeed, but shows an obvious loophole... if Russia wanted to it could have created a 3 ton ground launched cruise missile with a range of 6,000km and called it a strategic weapon... would be cheaper than an ICBM and could be used to attack targets in Europe and would not be effected by the INF treaty because its range exceeds the specification.
But they didn't because the US could do the same and render the INF treaty useless.
If Russia had the obligation to get China as a 3rd party to START, then the US has an obligation to get France and the UK
to submit as well.
Why not Israel and Pakistan and India as well?
I believe it is radar, they can detect the trails of the subs even when very minimal. But don't take my word for it, I have not researched that enough.
There is talk that radar can detect the small rise in sea level above a submerged submarine as it passes, and there is a trail an IR system can detect where water from different depths is churned up by the passing of a submerged submarine stirring up different temperature water from different depths in its wake... forming a pattern that can be seen from space.
In combination with Sonar sensors on the sea bed and other assets around the place all that information can be combined to keep a general track of known sub positions.
Wont be perfect but should be very useful...