Liquid propellants are generally less stable than solid fuel. I had read in multiple places (from reputable sources) that you generally couldn’t keep liquid missiles permanently fueled like that. The propellants are extremely corrosive and dangerous.

But you are right that the Titan II is liquid fueled and was kept permanently fueled in the silo. I’m not entirely sure how to resolve those two facts. The Wikipedia page about the Titan II does mention multiple accidents and fatalities related to propellant leaks, so I’m guessing that they were just more risky to operate?

There was an incident where a technician dropped a large socket down a silo that impacted the side of a Titan missile and set off a chain of events that ended in an explosion that nearly detonated a nuclear bomb on US soil.

The Damascus Incident[0]. There's a book called Command and Control: Nuclear Weapons, the Damascus Accident, and the Illusion of Safety by Eric Schlosser that details the incident, and a PBS based on the book about it.

[0] https://en.wikipedia.org/wiki/1980_Damascus_Titan_missile_ex...

I was hoping this book would be a recommended. It really, really focused, reinforced is really not the right word to use here, my views on nuclear weapons.

This should be required reading.

The main problem with traditional liquid fuelled rockets is keeping the propellant cold. It’s not feasible to keep a rocket with liquid oxygen fuelled for long periods. The Titan missiles use hypergolic fuel which is more storable, but also extremely toxic and volatile. More than 50 people have been killed in accidents involving this rocket.

It helps if you think of liquid-fueled rockets relying on cryogenics as something entirely different than those using hypergolics. Cryogenics can't sit there for a long time but hypergolics can.