The Shock Trial is on the way out
The U.S. Navy is debating the utility of shock trials. Shock trials test how ships handle undersea explosions, giving sailors a better understanding of how the vessel will hold up in battle. In technical terms, shock trials make the hull vibrate to see how the installed and integrated components respond to ensure the ship can continue to fight. Once a regular feature of naval shipbuilding, the Navy’s enthusiasm for this real-world simulation of battlefield conditions has dwindled over time. Why?
There are a variety of reasons the Navy wants to move away from shock trials. Shock trials are expensive, only taking place under a constrained set of conditions. Weather conditions and environmental concerns make scheduling difficult. Even worse, busy shipyards make it challenging to bring a ship in for timely repairs after the shock trial occurs.
Shock trials do break ships. Today, most Navy ships are mosaics of various different shock-resistant specifications. Critical components are built to tough “Grade A” specifications, and they are ostensibly robust enough to keep working after a shock event. Other, less critical, components are built to “Grade B”, and, while they are not guaranteed to work after a shock, testers don’t want those pieces of equipment to break loose and risk hurting a sailor. Operationally, that means non-mission critical Grade B gear must either be dismantled or tested and repaired post-shock.
Those preparations are no trivial task—dismantling every wall-mounted TV screen from America’s newest aircraft carrier, the USS Gerald R. Ford (CVN 78), takes time away from other priorities. The aircraft carrier USS Gerald R. Ford, for example, is trying to fit shock trials into schedule already jam-packed with operational testing and maintenance activities. As such, a shock trial poses a significant challenge that may, potentially, force the rescheduling of even more critical shipboard training and tests.
America’s Navy is evolving away from real-world shock trials. In the past, first-in-class warships were subjected to a shock trial. Times have changed; on only two of the last 11 ship classes or Flights has the first ship been tested. Instead, most often the second or third—or even later—vessels have been shocked. In fact, the Virginia class nuclear submarine—a multi-billion dollar mainstay of America’s undersea battle fleet—has never been shocked at all.
So why is the shock trial losing favor? Is it something that can be cut from naval shipbuilding, or is it a differentiator, another step that makes U.S. Navy ships better than anybody else’s?
What Do Shock Trials Do?
Shock trials help the Navy understand how things aboard ships respond to the sudden shock—or vibrations—that can be generated by an explosion, collision or other catastrophe.
Resiliency to shock matters. In 2017, when the USS John S. McCain was holed by a collision with a cargo ship, “racks and lockers detached from the walls and were thrown about, leaving jagged metal throughout” impacted areas, hindering escape from damaged berthing areas.
While shock trials do not model collisions, they can help identify vulnerable fittings, modifications and other often-overlooked features that could, when severely jolted, mean the difference between life and death aboard ship.
With modern computers, many shock-related vulnerabilities can be modeled, eliminating the requirement for full-scale tests. While the mathematics of modeling shock transmission aboard surface ships is daunting enough to require real-world testing, submarines only require smaller-scale tests and modeling.
This pull-back from submarine shock testing has been affirmed in the latest annual round of DOT&E test reports. These reports—which are normally a source of ugly news about America’s most modern weapons—were positively sanguine about the lack of Virginia class shock testing activities. In two separate sets of live fire tests, Tube Stiffened Models were used to evaluate both shock and pressure loading after explosions. The data gathered in these events will be sufficient to inform survivability models for a range of new underwater assets.
This type of testing has proven to be reliable in real life. When the Los Angeles class Attack Submarine USS San Francisco ran into an uncharted seamount at high speed, the ship didn’t sink and the crew managed to get the sub back into port under it’s own power.
The challenge is to get modeling for ships—which exist at the dynamic interface between the sea and sky—to match the fidelity of relatively simpler models used to test and challenge America’s undersea designs.
Ultimately, shock testing injects an element or reality into modeling. Untested, under-validated models are useless. Shock tests can also help understand the impact of modifications and “on-the-fly” innovation, and testing how simple or oft-ignored things like bunks and cables respond to shock—little things that may not save a ship but may well save a few more lives. So while shock testing may be on the way out, it may be wise to keep on plowing data into the models for a few more years.