bobbymike said:I would go with a D5 diameter sized replacement with a longer first stage for global range from CONUS.
The USN and USAF use very different propellants for their ballistic missiles. The Navy propellant allows for higher impulse density, for better performance in a smaller missile... at the cost of being somewhat twitchy compared to the staid USAF propellant. The USN probably wouldn't be able to meet performance requirements with USAF propellant; the USAF would probably be unwilling to use the less stable Navy propellant. And the difference in propellant is sufficient that you couldn't simply put different propellants in the same missile hardware. So there's little utility in common booster stages.
That said... no reason they couldn't use the same RV's. No reason they couldn't use the same propulsion module, guidance system and software.