When President Dwight D. Eisenhower spoke of the influence of the military-industrial complex nearly 60 years ago, he was issuing a warning, not giving investment advice. But he could’ve been, because, since then, military spending in the United States has remained as enormous as a giant aircraft carrier.

Today, it amounts to about $700 billion a year — roughly one-sixth of the federal budget — and accounts for much of the annual sales of such stock market stalwarts as General Dynamics, Lockheed Martin, Northrop Grumman and Raytheon.

That combination of federal dollars and corporate heft may represent an opportunity for investors who don’t mind profiting from warfare. A modest bet on a mutual fund or exchange-traded fund that buys military contractors and aerospace companies may help buffer the deep recession brought on by the coronavirus.

Military contractors are, to a large extent, “selling to one major customer — the U.S. government,” said Jonathan W. Siegmann, manager of the Fidelity Select Defense and Aerospace Portfolio. “That customer buys things much differently from anyone else in the world.”

That gives the companies’ income stream some unique characteristics, he said: “The economics can be quite profitable — the government will pay for your R.&D. and capital expenditures — so I believe you can get a better risk-adjusted return. But it’s not a technology sector that’s going to sustain double-digit growth.”

All sectors have lately fallen because of coronavirus and its daunting economic repercussions, but some military stocks have fallen less. This year through March 31, for example, Northrop Grumman dropped 11.66 percent, including dividends. That compared with a 19.6 percent decline for the S&P 500 — and a 53.59 percent decline for Boeing, the troubled aerospace giant. The S&P Aerospace & Defense Select Industry Index, to which Northrup and Boeing both belong, fell 29.83 percent.

The tight link with the economic growth of aerospace and commercial airline companies is why Byron Callan, an analyst at Capital Alpha Partners in Washington, D.C., suggests buying stock in individual military contractors and not a mutual fund or an E.T.F.

No fund invests only in military contractors, he said. “The funds commingle commercial aerospace and defense, and those are distinct markets.” (Note that following Mr. Callan’s advice would mean picking individual stocks and sacrificing a fund’s diversification.)

Even with commercial-air exposure, an investment in a military-and-aerospace fund might still hedge against hard times, including the worldwide recession that, according to the International Monetary Fund, has already begun. As consumers and companies cling to their cash, the U.S. armed forces will keep buying nuclear submarines, fighter planes, missiles and drones.

“Defense budgets are determined by the threats against the country, and the U.S. generally spends what it needs to,” said Christopher A. DeNicolo, a director and defense and aerospace analyst for Standard & Poor’s. “We have by far the largest military budget in the world.”

Ranking a distant second behind the United States is China, which, in 2018, spent $250 billion, according to the Stockholm International Peace Research Institute.

Military contractors in the United States make about $180 billion a year in sales abroad. Sheila K. Kahyaoglu, an aerospace and defense equity analyst at Jefferies, said several of the biggest contractors generate about one-fifth of their revenue overseas.

Fund investors have only a few options if they want to make a focused bet on military spending. The single actively managed fund is the one run by Mr. Siegmann for Fidelity. As is typical, he invests in both military contractors, like Northrop Grumman, and aerospace companies, like Boeing. As is also common, his portfolio is concentrated: The top 10 holdings — all domestic companies — account for 72 percent of the total assets.

The fund, with an expense ratio of 0.75 percent, returned an annual average of 10.65 percent for the 10 years that ended in March.

The indexed offerings in this niche include the Invesco Aerospace & Defense E.T.F., the iShares U.S. Aerospace and Defense E.T.F. and the SPDR S&P Aerospace & Defense E.T.F.

Each replicates a different index, though their compositions are similar. All include Lockheed Martin, Northrop Grumman, L3Harris and General Dynamics among their top stakes.

The largest of the three, the iShares offering, tracks the Dow Jones U.S. Select Aerospace & Defense Index, lately made up of 33 U.S. companies.

Christopher Dhanraj, head of iShares investment strategy at BlackRock, said the index aims to reflect the economic growth generated by military spending. “The U.S. military doesn’t just have boots on the ground,” he said. “It’s investing in cyberwarfare and other kinds of innovation.”

The iShares E.T.F., with an expense ratio of 0.42 percent, returned an annual average of 10.34 for the 10 years that ended April 1.

With all four of these funds, an investor will end up with shares of a few dozen steadily growing industrial companies.

“These are large, stable companies with multiyear pipelines of products,” said Todd L. Rosenbluth, director of E.T.F. and mutual fund research at CFRA, an investment research company.

“It’s a relatively concentrated part of the market — the companies that have been dominant remain dominant.”

That predictability is a key to the investment appeal, said Ms. Kahyaoglu, the Jefferies analyst.

“There’s very little movement in the earnings stream for these guys,” she said. “In the next two years, the defense budget is locked in.” She said she expects that the outcome of the presidential election will have little short-term impact on military expenditures, though big changes could take place over longer periods.

Military purchases usually come with long lead times and high prices, said Robin S. Lineberger, global aerospace and defense industry lead for Deloitte Consulting. “The last big contract I’m aware of for submarine build out was about $20 billion.”

In December, the U.S. Defense Department reached an agreement with General Dynamics for the company’s Electric Boat subsidiary to build at least nine Virginia-class attack submarines. Delivery is expected from 2025 through 2029.

While the military industry isn’t a fast grower these days, it has lately expanded into a capacious new market — space. Many modern technologies depend on satellites, and protecting those has become a priority, Mr. Lineberger said. Satellites were once seen as too distant to attack, but several countries have shown the ability to shoot them down.

Politics necessarily influences a market in which security policy and federal spending loom so large. Geopolitics often determines what’s bought — will it be hypersonic missiles or Joint Light Tactical Vehicles? — while national politics can influence how much and from whom.

These days, both political parties in the United States support robust military spending, but their priorities can differ, said Loren B. Thompson, a consultant to military contractors and chief operating officer of the Lexington Institute.

“Under Obama, the national defense strategy was focused primarily on terrorism, and that didn’t require a lot of new weapons,” Mr. Thompson said. “So demand for weapons was trending downward. But the moment Trump gets in, it’s all about China, which requires more weapons.”

One thing that won’t change is that this industry enables war-making and killing. That’s likely to give some investors pause.

None of the mutual funds of Calvert Research and Management own companies typically classified as military contractors, said John H. Streur, the firm’s chief executive. Calvert, an Eaton Vance subsidiary that emphasizes environmental, social and governance considerations, doesn’t oppose owning military contractors on principle, he said, because countries do have to protect themselves.

“We’d all prefer the world get rid of its weapons, but that’s not realistically going to happen,” he said. “In that context, one can get comfortable with the concept that it’s ethical to invest in some of these companies.”

For Calvert, a crucial distinction is the kinds of weapons a company makes.

“Cluster munitions or systems for the delivery of those are something we’d avoid,” he said. “They’re indiscriminate and unintentionally harm civilians. We’re also very against land mines, which don’t get picked up when war is over.”

Lockheed Martin, for example, makes weapons capable of delivering cluster bombs and thus is a company Calvert would shy from, Mr. Streur said. On top of this, it’s facing a federal lawsuit over violations of the False Claims Act, he said.

Lockheed Martin would not comment on whether the company makes weapons that are capable of delivering cluster bombs. In a written statement, Jarrod P. Agen, a Lockheed vice president, said the company “does not develop or produce cluster munitions, as defined in the 2008 Convention on Cluster Munitions.”

Implicit in Calvert’s approach is the idea that military spending is about managing risks to the United States. Investors considering one of these funds should be aware that they’re taking on risks of their own.

With an offering focused so narrowly, you’re making a “trifecta bet,” said Ben A. Johnson, director of global E.T.F. research for Morningstar.

You’re wagering that three hunches are right — that military spending will increase, that you’ve picked the right fund and that the story you’ve identified isn’t already reflected in defense-and-aerospace stock prices.

“This is a very risky thing to try to do,” Mr. Johnson said. “The odds are you’re going to get it wrong.”

“I’m not trying to preach abstinence,” he said. “People are tempted to tinker, but set aside a small tinkering pot. Don’t do that with your overall asset allocation.”