Tonnage Cannot Fully Define Fleet Lethality

The U.S. Navy incorrectly measures its fleet’s lethality. The service uses tonnage as a proxy for strength, but warfare capability is built by sensor-shooter networks, not mountains of steel. The Navy should update how it measures and understands the strength and size of its fleet. 

Sizing up the Fleet

Naval power thought leaders such as Eric Labs of the Congressional Budget Office (CBO) measure the fleet by ship count, budget, and tonnage. At the Office of the Chief of Naval Operations, binders bounce open to charts counting vertical launch system (VLS) tubes to carry missiles. And from watch floors around the world, intelligence teams closely follow the technical advances of People’s Liberation Army Navy warships.

There are many ways to measure fleet capability. But tonnage is the accepted stand-in for power. 

“Displacement is commonly used as a general proxy for the capability of a ship,” analysts wrote in a CBO report on the Navy’s 2025 shipbuilding plan. “Thus, a fleet that totals two million tons in displacement is considered to be more capable than one . . . that totals half that amount.” Analysts at the Center for Strategic and International Studies point out, accurately, that larger ships have more range, speed, and power.  

The problem with this measure is that tonnage drives cost, not capability. At first glance, that does not necessarily make it wrong: Cost itself could be used as a proxy for capability. Logically, a ship with $100 million of sensors and weapons must be more capable than if it had only $10 million of the same. But high cost itself does not make the Navy’s fleet match up effectively against adversaries. In fact, cost is useless to compare fleets built by different industrial bases, because building a ship in China costs much less than building one in the United States or Europe. Chinese cruisers that roughly match U.S. destroyers in tonnage and weapons are a fraction of the cost. 

Measuring Tonnage Drives Cost

So archaic a measure is tonnage that the word originates from “tun” in Middle English. It referred to a cask of wine and was used as a common measure of a merchant ship’s capacity. Fresh from their muddy victory at Agincourt, unaware of the New World’s existence across the Atlantic, Henry V’s 1422 government offered the first written guidance to measure ships by size. 

Today in the United States, welding and integration labor are the top drivers of shipbuilding cost, and bigger ships take more welders and technicians to build. As tonnage increases, so does the complexity of welds. Bigger ships need more structural supports. Size determines complexity across the ship’s systems, such as for control wiring, ventilation, and defensive payloads. Together, these cost drivers mean that heavier ships are more expensive ships.

Because congressional experts know tonnage drives up costs, Navy designers sometimes are afraid to propose a heavier ship design. They pack extra capabilities into the same hull, driving complexity as installation density increases. This method requires the most specialized labor, complicates maintenance, and saves money only on steel, which is the cheapest input. 

Prioritizing tonnage for the whole fleet also drives costs higher. When construction is limited to one or two ships per year for most ship classes, the only way to ensure more capability is to bake in large, heavy, expensive designs during the requirements process. Navy planners already have enough incentives to make choices that cause costs to spiral: adding payloads and survivability systems creates consensus in the Pentagon that a ship will be highly capable. Many ship and submarine designs thus grow in weight by 20–50 percent relative to their preceding classes. 

As ships get heavier and more complex, fewer shipyards can produce them, and fewer suppliers can fabricate components. In addition to labor costs, the main constraint at most shipyards is on the size of ships they can assemble. Yards need a crane, gantry, or rolling transporter that can move the hull or lift heavy components such as a propeller or superstructure. Many smaller shipyards max out at hundreds or thousands of tons. In addition, they need a large slip and a deep draft in their harbor to launch a larger ship. These constraints can change, but for producers to adapt, it takes tens of millions of dollars of capital investment over years. 

Most of the capable shipyards operate under cost-plus contracts, so they are happy with bigger, more-expensive vessels that other yards cannot develop the expertise to competitively build. With a single yard producing most U.S. Navy warship classes, it should not be surprising that the United States cannot build more ships. 

Over the past decade, the U.S. industrial base has increased its shipbuilding capacity by 80 percent when measured by tonnage. Costs have grown substantially. But the fleet’s combat and regeneration capabilities have atrophied. Ship tonnage is therefore a very important measure—not of capability, but of cost. 

Alternative Measures of Naval Capability

Fortunately, as shown in the figure below, naval thinkers measure the fleet’s capability in many ways. 

Strike capacity is an important measure—one that directly counts lethality, rather than deadweight cost. In the charts above, several metrics across surface, subsurface, and air warfare triangulate effectively to measure fires that the U.S. Navy fleet can deliver. 

These metrics tell a much clearer story than tonnage, but they ignore key elements of naval capability. A force optimized for them would likely include many destroyers and carrier air wings—platforms that offer many missile tubes and target engagements. But this force would deprioritize submarines, which have fewer missiles, and would extend the life of aging cruisers, which seems like a bad idea.

In addition to counting missiles and torpedoes, analysts should use metrics that can count targeting capability. Without the ability to target adversaries, large missile magazines are worthless. 

One metric could be the number of sensors. Since many sensors are concentrated on single platforms, this measure might best be expressed as the number of square nautical miles all the Navy’s platforms simultaneously cover. Under this method, only the longest-range sensor on a given platform would count. This is a challenging metric to develop, however, since sensor ranges are classified, and passive sensors do not really have their own range like active ones do. The number of reconnaissance hours in the air, the number of satellite passes, or the number of patrol days for ships or submarines all could be tallied to demonstrate the Navy’s ability to deploy sensors that can hold an adversary at risk. 

Since the Navy already does a good job of counting shooters (missiles, torpedoes, etc.) and platforms (ships, submarines, and aircraft), it also needs a way to assess its ability to network these systems together. Communications equipment must connect the sensors to the shooters. Total bandwidth capacity on each part of the spectrum could be one measure. Another could count communications systems or tally the time it takes to identify, pass, and engage a target. 

The Navy also could measure the number of payloads deployed. Payloads are the reason platforms exist. Measuring naval power by tonnage or number of ships leads to misplaced satisfaction about the exorbitant cost of a fleet. Cost could instead be measured as the expense per payload deployed. A lethality ratio such as missiles per ship ton, or per platform dollar, should measure capability. 

This lethality ratio is useful when comparing similar platforms. New surface combatant designs, such as for a destroyer, cruiser, or frigate, should compare it to historic ratios for similar ships. A $1 billion surface combatant with 32 VLS cells, for example, costs $31 million per cell. A $40 million warship with 8 cells is paying only $5 million per VLS cell. 

Distributed Maritime Operations & Tonnage

Fortunately, the Navy has already written doctrine that counterbalances the usual focus on tonnage and missile cells. Distributed maritime operations (DMO) calls for a disaggregated fleet architecture of many smaller warships. Some of them will be unmanned.

Decision frameworks that prioritize payloads, sensors, and missiles—the essential threads of a maritime kill web—will help requirements officers design simpler warships. These simpler warships will be easier to produce, and when built at scale they will deploy many more payloads into the Pacific than today’s fleet of large, expensive warships. DMO requires this kind of fleet. 

Small unmanned surface vehicles, although not open-ocean ships, are the readiest proof point of this framework. The Navy’s global autonomous reconnaissance craft deliver many more payloads, and cover many more square nautical miles with sensors, than does any single aging warship. 

To achieve DMO, the Navy must adopt measures of capability consistent with kill-web warfare. Tonnage should still be measured, but with an eye to reevaluating the construction of expensive mountains of steel.