The U.S. Navy could buy older civilian merchant ships on the cheap and convert them into floating arsenals. The concept, outlined in the U.S. Naval Institute, envisions adding dozens—if not hundreds—of multiuse missile silos to the ships to provide additional firepower to the Navy while it struggles to reach its 355-ship goal. The idea is an attractive one but has a number of issues under the surface.
The heart of today’s U.S. Navy’s surface ship firepower, which lives on destroyers and cruisers, is the armored missile silo. The –class guided missile destroyers each carry 90-96 , the -class guided missile cruisers carry 122 Mk. 41 silos, and the Zumwalt class carries 80 Mk. 57 silos. Each of these silos can carry one long-range anti-ballistic missile interceptor, surface-to-air missile, land attack cruise missile, anti-submarine rocket torpedo, or anti-ship missile each, or even up to four smaller short range air defense missiles. This versatility makes the fleet endlessly adaptable. A destroyer can carry all surface-to-air missiles, all anti-ship missiles, or a mix of all types.
There are a few catches. These silos are enormously expensive to add to the fleet: Arleigh Burke–class destroyers cost somewhere in the neighborhood of $1.5 billion each, meaning each silo costs about $15 million each to put to sea, missile not included. Also, once a silo is loaded in port the missiles can’t be swapped out at sea. A destroyer that inadvertently brings a belly full of anti-ship missiles to a submarine hunt must go back to a friendly port and swap missiles.
An article from the U.S. Naval Institute . One of the main barriers is hull cost. Why not buy secondhand commercial tanker hulls for $25 to $50 million each (as opposed to $1.5 billion for a brand new destroyer) and then strap missile silos to the deck? These silos could then be datalinked to the rest of the fleet, providing firepower on demand for the real warships. The article makes the case that 30 to 50 missile silos per ship is a good number, and that "[converting] 10 to 15 cargo ships would give the fleet between 300 and 750 missile cells at a fraction of the cost and time for new-build surface combatants.”
Civilian ships have long served in the Navy, often as auxiliary, second-line ships meant to free up warships for more vital missions. Now, technology could allow civilian ships to be fitted with the latest technology to engage adversaries from up to hundreds of miles away. The Navy already has ships in the fleet that are former merchantmen. The hospital ships are ex-oil tankers fitted to provide medical services for up to 500 personnel.
Hospital ships are not warships, however, and the “commercial ship turned warship” concept could have complications. Warships are built to a very high standard, designed to take physical punishment and continue fighting. Civilian ships aren’t meant to fight and are built to a less rigorous standard. In 2016, the aluminum-hulled high-speed trimaran Swift was while supporting UAE forces involved in the war in Yemen. As a civilian ship pressed into military duties, Swift likely did not have the built-in resilience of purpose-built warships and a dedicated damage control party to limit the spread of damage.
Commercial ships are also slower than warships, which would drag down the fleet's effective top speed, limiting its ability to respond to situations. Older commercial ships could have less reliable propulsion and other systems. Finally, their resemblance to ships in civilian service could make those civilian ships targets, as an adversary tries to hunt down and eliminate these heavily armed ships.
Still, if the Navy can accept or mitigate these issues without the need for expensive, bureaucratic, time-consuming fixes, it can vastly increase its floating firepower. For the price of one new destroyer with 96 missile silos it could easily have up to 30 ex-commercial vessels with 50 missiles each. One destroyer can only be in one place at a time, but 30 ex-commercial vessels could be in 30 different places all over the globe. Is that an acceptable trade-off? That’s for the Navy to decide.