John F. Lehman, a former Navy Secretary and current adviser to Mitt Romney’s campaign, testifies before Congress in 2004. Photo: AP/Lawrence Jackson

Edited 4:55 p.m.

Republican presidential candidate Mitt Romney has vowed to boost the size of the Navy by roughly 15 percent as part of a broader defense buildup. “Our Navy is smaller now than at any time since 1917,” he complained in Monday night’s debate. “That’s unacceptable to me.”

But for one of Romney’s most important advisers on Navy issues, a man who oversaw a massive naval expansion for Pres. Ronald Reagan, there’s more at stake than U.S. national security. John Lehman, an investment banker and former secretary of the Navy, has strong and complex personal financial ties to the naval shipbuilding industry. He has profited hugely from the Navy’s slow growth in recent years — raising the prospect that he could make even more if Romney takes his advice on expanding the fleet.

That doesn’t mean that a bigger or better Navy is necessarily a bad idea. But it does complicate Romney’s claim that a larger Navy would merely be “matched to the interests we need to protect.” A bigger maritime force has the possibility of personally enriching one of the candidate’s top advisers. In fact, it already has.

Lehman is the founder and chairman of J.F. Lehman & Company, a private equity firm. He also sits on several corporate boards.

Lehman invested in a government-backed “Superferry” in Hawaii — a business that ultimately failed, but not before boosting the standing of Austal USA, an Alabama shipbuilder that constructed the ferry service’s ships. Austal USA’s rising fortunes in turn benefited international defense giant BAE Systems, which then bought up shipyards owned by Lehman in order to work more closely with Austal USA.

When all was said and done, the roundtrip deal helped net Lehman’s firm a reported $180 million. And besides that, Lehman continues to own shipyards that do lucrative maintenance work for the Navy. Even leaving aside the intricate ferry-and-shipyard series of deals, Lehman still stands a decent chance of profiting from the naval buildup he is helping to plan.

Lehman, through a Romney campaign aide, calls any suggestions that he benefited from shipbuilding operations “kind of amusing.” Lehman says he lost enormous sums of money on the Superferry deal, rather than earning it.

But Ryan Sibley — an editor at the Washington, D.C.-based watchdog Sunlight Foundation who has closely tracked the former Navy Secretary’s investments — says that ”Lehman’s involvement with the Superferry shows that he is no stranger to using personal connections to influence costly decisions.”