Chief of Naval Operations (CNO) Admiral John Richardson has voiced concern about fleet operational restrictions imposed by the Navy’s ballistic-missile defense (BMD) mission.  The CNO explains that the BMD ships are restricted to confined operating areas—“little boxes,” as he puts it. His concern appears not to be with the BMD mission, but rather that with only 280-some ships, restricting the movements of BMD assets means that there are other important missions elsewhere that the Navy cannot fulfill.
The 355-ship force is a goal—and a distant one at that. The actual size of the Navy in recent years has fluctuated between 270 and 290 ships.
To get to 355, the Navy’s 2019 ship-building plan proposes an eventual composition of 12 aircraft carriers, 12 ballistic-missile submarines, 66 attack submarines, 104 large surface combatants, 52 small surface combatants, 38 amphibious warfare ships, and 71 combat logistics and support ships.  But the Congressional Budget Office (CBO) notes that the proposed construction and retirement schedules “would not meet [the] goal of 355 ships any time over the next 30 years.”  The Navy has responded by announcing service-life extensions for some destroyers and attack submarines to “reach 355 ships in 2034.”  The cost to build and operate the proposed fleet would average $109 billion per year (2018 dollars) through 2047, “at least one-third more than the amount appropriated for fiscal year 2016 for today’s 275-ship fleet.” 
This makes the plan’s completion seem very unlikely. Indeed, Representative Adam Smith (D-WA), incoming House Armed Services Committee (HASC) chair, has noted that the Department of Defense’s current $717-billion budget is not likely to reach that size again any time soon. Smith expects lawmakers increasingly will focus on military capabilities rather than numbers of ships, aircraft, or weapon systems. HASC has urged the Navy to consider options beyond new construction to grow the fleet.
Conversion not Construction
One option would be for the Navy to convert readily available merchant hulls into missile-armed Navy ships.
CBO analyst Eric Labs points out that:
“Measuring relative naval power is a difficult task. Of the measures CBO used, the number of VLS cells is arguably the most meaningful because it represents the missile firepower of the fleet, which serves as a proxy for its offensive and defensive capability. . . . A weakness of using [this number] however, is that it does not capture the capability of the Navy’s most potent conventional weapon system—the aircraft carrier and its embarked air wing—nor that of the Navy’s amphibious warfare ships. However, there is little difference in the [proposed] number of aircraft carriers among CBO’s alternatives until the 2040s.” 
Former Under Secretary of the Navy Bob Work appears to concur on the utility of VLS-cell-number metric because it emphasizes fleet offensive and defensive capability over simple hull numbers. 
Because the number of aircraft carriers in the fleet will not increase until the 2040s (if then), the question becomes how to add VLS cells (and missiles) to the fleet sooner. Modernizing and modifying existing ships is a necessary first step. For instance, adding missile systems to amphibious ships could increase the VLS-cell inventory by around 270. 
More cells are necessary but not sufficient. Additional hulls are needed to compete with near-peer adversaries, and converting merchant ships into VLS missile-cell carriers could provide an economical complement—although not a complete alternative—to new construction.
Options include International Maritime Organization–compliant double-hull tankers and container ships. Given their size, either type probably could accommodate tactical ballistic missiles in addition to ship-launched cruise missiles. Container ship conversion into a “missile merchant” would be easier and probably less costly if VLS modules were housed in special ConEx Boxes or stacked in container cells. On the other hand, Mercy- class hospital ships are converted tankers in which the medical spaces were dropped into the open hull; similarly installing conventional VLS modules on board a modern tanker would offer improved survivability. 
It Floats—But Will It Fight?
By leveraging existing combat systems and “kill webs,” missile merchants would act as on-demand remote magazines—not unlike the arsenal ship concept (more on that below). Advances in high-performance computing, software virtualization, and composite materials enable proven, existing systems such as cruise missiles to fit into International Organization for Standardization–compliant ConEx shipping containers. This modular form-factor allows for rapid and low-cost outfitting of container ships and plug-and-play compatibility with existing Navy and Joint combat systems. These technologies increasingly leverage offboard targeting data, allowing for missile merchants to contribute to the fight without requiring expensive sensor suites.
Such ships can increase not only the capacity of the fleet but also its capability. In particular, the Navy faces a range challenge from current and emerging unmanned aerial systems and ballistic and cruise missiles. The current carrier air wing has a range of 450 nautical miles (nm). Even when the MQ-25 Stingray tanker reaches initial operational capability in 2027 , the air wing will only have a range of around 700 nm—about half that of many antiship cruise missiles. VLS-configured or containerized missile systems would dramatically (and comparatively inexpensively) increase the damage a strike group could inflict before closing to launch aircraft.
How Many? And How Much?
Cargo ships are bought and sold through a network of ship brokers, with the largest based in Europe and Asia. Trade publications such as Tradewinds , Lloyds List , Marine Log , etc., show that the nominal cost to acquire container or double-hulled tanker ships could be between $25 and $50 million per hull depending on size and where they were constructed.  (Any major conflict in the Pacific will significantly reduce international trade, which could make a large number of commercial platforms suddenly available at a fraction of the cost of building a new warship.)
Because the expensive sensor suites will be off-hull, the cost to convert such ships to missile platforms should be modest, assuming the employment of standard Mark 41 VLS 8-cell modules or purpose-built ConEx boxes. Using standard 20- or 40-foot-long freight containers offers the advantage of several different loading systems and intermodal handling systems ashore.
It’s the People, Not the Machines
To crew these ships, reserve detachments could provide one option, although Navy Captain Chris Rawley, a reserve surface warfare officer, has suggested that a “hybrid” crew model might be best:
A handful of warships in the U.S. Navy, including USS Ponce (AFSB(I) 15), two flagships, and submarine tenders . . . are commanded by a commissioned naval officer, though their navigation and engineering functions are primarily conducted by [civilian mariners]. This hybrid crewing approach enables them to conduct or command offensive operations in accordance with international law.
One of the Navy’s key vulnerabilities today is its inability to replace combat losses rapidly. The combination of reduced shipyard capacity and long construction times means the Navy will have to fight with whatever ships are in or near commission. The current shipbuilding plan does not address this problem, but converted merchant ships could offer a solution.
Rather than trying to maintain reserve ships in the so-called Ghost Fleet, the Navy could ensure surge-production capacity for missile and drone systems. Rapid conversion of merchant ships combined with significant output of offensive weapons would cut the time required to supply new combatants to the fleet from years to months. With practice—and a stock of containerized weapons systems on hand—the conversion time possibly could be reduced to weeks.
Using the hybrid crewing model, reservists could crew the ships and operate the weapon systems, focusing their normal peacetime training commitments on their possible wartime missile-merchant duties. (Weapon system reservists should be able to train at home stations since most training could be designed to use simulators.) The annual two-week, active-duty period would be dedicated to team training on board a ship at sea.
Sizing the Magazine
The question of how many missiles each ship should carry invites a hedged response: enough to be of interest to the adversary, but not so many as to mimic the arsenal-ship concept . When they were proposed, those floating magazines were considered risky, holding too many eggs in each basket. If only a few large merchants became missile ships with, say, 100-plus missiles per hull, an adversary could concentrate attacks on these few ships, roughly equivalent in value (at least by the VLS-cell metric) to destroyers and cruisers.
The Navy might therefore consider missile merchants “too important to lose,” starting a spiral of engineering changes, defensive system upgrades, and cost increases. On the other hand, arming them with too-few weapons does not add much punch and does little to complicate adversary planning. A detailed campaign analysis is warranted, but our rough estimate of the “just right” number is 30–50. 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.
Missiles Need More than VLS Cells
Arleigh Burke –class destroyers were designed around their weapon systems. This results in fine warships, but at great cost in time and money. The missile merchant would rely instead on weapon systems built as modular units—not only the missile launchers, but also the sophisticated computing assets that support them. Commercial ships have the space but may not have the electrical power or cooling infrastructure to support standard processing equipment. Virtualization, which digitizes functions that physical computer components would otherwise do, can shrink whole combat systems to the size of desktop computers and reduce their support needs. This comes at a processing-power cost, but the missile merchants will receive their targets from sensors on aircraft and conventional surface combatants, reducing computing demand.
Missile merchants will have to rely on reduced susceptibility to detection and targeting for survivability. As offensively capable naval vessels, missile merchants would need to be marked as United States Ships, flagged, and named—a problem in the face of electro-optical sensing. But many targeting systems rely on inverse synthetic-aperture radar, which produces a low-resolution image of its target for identification, revealing only a simplified shape. In heavily trafficked areas, a missile merchant without sensor masts would be hard to discern from other merchant ships at range. Electronic emissions that could be correlated to U.S. Navy assets pose risks that must be mitigated as much as possible. Automated ship reporting systems should be used judiciously.
While it is true that converted tankers and container ships will lack many of the defensive systems to defeat modern naval weapons, they will require only small crews of perhaps 30 sailors each. The Navy can experiment with inexpensive ways to harden these ships. Ships in the 30–50,000 dead-weight ton range would possess cargo capacity well in excess of that needed for the combat systems. Even a small container ship will have hundreds of empty containers. The Navy could experiment with different types of fill to absorb the energy of enemy weapons— anything from large sandbags to expanding foams. Much as World War II Q-ships sometimes carried buoyant cargoes to make them survivable, the Navy today could mount the outer rows of containers as inner hulls. If only the inner two rows carry weapons, up to four on each side could be configured as protective layers and perhaps reserve buoyancy.
Damage control could consume the efforts of a minimal crew, but—with some additional cost—automated systems could be installed. Drawing enemy fire could become an important function, perhaps protecting higher value, more-densely manned combatants.
Distribute Lethality Today, Not Tomorrow
Converted merchant ships can serve as durable, inexpensive weapons "trucks." Given the interchangeability of modern containers, these converted ships could become among the most easily upgraded systems in the fight, at a fraction of the cost and time required to design new ships around new systems. The Navy should start experimenting with the concept immediately.