Not sure if this should be here or in "Land". In any case, consider the Texas Tower radar stations used off the Atlantic coast of the US from the mid-50's to the early-60's. Now, if ICBMs had not been developed, might these have continued, with upgrades as the drilling rig technology improved? It further occurs to me that these would be prime targets for early take-out in an attack, so enhanced, or developed, one with self-defense capabilities, both anti-ship and anti-air, would seem logical. So, to save procurement costs and development time, use existing tank turrets for the anti-ship role and add suitable AAA or SAM installations; you could, conceivably, also use turrets from de-commissioned big-gun destroyers or cruisers. Mind you, you'd also likely need to take precautions to prevent a repeat of what happened to Texas Tower 4.