MQ-1 PREDATOR drone. America's weapon of choice in the war on terror is due for retirement. But who will replace it? Image source: U.S. Air Force.

It's been more than a decade since America declared a "War on Terror." Over these 10-plus years, America has fought wars in both Iraq and Afghanistan, ended "combat operations" in both, deployed troops in less official capacities in several additional conflicts, and then sent troops right back into Iraq, while keeping them in Afghanistan continuously.

Despite our best efforts, securing "peace in our time" has remained elusive, and defense companies, and defense stocks, remain as relevant as ever. As Americans, we're all entitled to hope for the best. But as investors, it's probably more realistic to continue to plan for the worst -- and continue to invest in defense stocks as long as a need for them is foreseen.

To that end, we've polled a few of the best minds here at The Motley Fool, asking which defense stock they think is the most important one to own for the next 10 years. Here's what they had to say.

Dan Caplinger: It's easy to forget that Boeing (BA -0.23%)

Boeing has had its share of difficulties in dealing with defense budget cuts, with its competitive strategy having led to some questionable decisions on key projects. For instance, moves like Boeing's low bid to handle the KC-46 refueling-tanker aircraft project have resulted in big charges and razor-thin profits at best on defense business, as heightened competition makes it more difficult to win contracts in the first place. Still, as geopolitical concerns mount, it seems increasingly likely that tough budget conditions will get better, and Boeing will be in a position to capitalize.

Boeing's diversification between commercial and military products gives it a big advantage for investors who want exposure to both markets. Given the great outlook for commercial aerospace in the next decade, choosing Boeing is a clear way to play that market and to get defense exposure as a potential bonus.

Daniel Miller: When looking for long-term winners in defense stocks, many investors overlook Raytheon Company (RTN). Raytheon has taken great strides to clean up its balance sheet by cutting its long-term debt in half over the last 15 years, and has extended maturities on the remaining debt. Management also refocused on its core defense business and contained costs, which enabled the company to do more with less net sales even during the Department of Defense's $1 trillion spending cut through 2021.

Image source: Raytheon's 2014 annual report.

Now that Raytheon is a much healthier company, there are two factors that make me believe holding the company over the next 10 years could prove valuable.

First, Raytheon's Patriot system missile defense is combat-proven and continues to sell well. Raytheon inked a $655 million contract to provide Kuwait with new units and a $160 million contract to another customer to provide Patriot Guidance Enhanced Missile-Tactical, or GEM-T, missiles. Lockheed Martin (LMT -1.93%) and Raytheon essentially form a duopoly in missiles, and international business will help fuel growth in the years ahead. 

The second reason I believe Raytheon is flying under the radar is its position in a hot market: cybersecurity. Raytheon continues to win new business and sees significant cybersecurity business opportunities globally.

Furthermore, Raytheon recently acquired Websense for a price tag of $1.9 billion. It was an expensive acquisition, but commercial cybersecurity is an attractive growth market, and Websense is a leader in commercial cybersecurity markets and advanced threat protection. Websense has a highly recurring subscription revenue model with strong profitability and will combine with Raytheon's existing business to become one of the broadest cybersecurity portfolios in the industry.

Over the next 10 years, if Raytheon continues to improve its bottom-line performance, it could become a much more lucrative business, provided the U.S. government's defense spending increases after 2021 and the company's cybersecurity business turns into a big winner.

Rich Smith: Last but far from least, let's not forget the elephant in the room, and America's biggest pure-play defense stock: Lockheed Martin.

Five years ago, when asked to name my top recommendation as a "core" stock for your portfolio, I picked Lockheed Martin -- and the stock has nearly tripled since. But I think that even after such an amazing performance, Lockheed Martin's run is not yet done.

It's priced today at less than 18.5 times earnings, and analysts give Lockheed Martin short shrift, predicting that the stock will grow earnings at only 8% or so per year over the next five years. Yet Lockheed Martin has consistently defied expectations, outperforming similar growth estimates in each of the past four quarters.

How has Lockheed Martin managed this? Primarily by dominating the defense business better than anyone ever had any right to expect. The biggest name in defense contracting not just in America but worldwide, Lockheed Martin builds the world's most popular fighter jet, the F-16 Falcon. The company also owns the world's top-selling combat aircraft that is not a fighter jet: the C-130 Hercules. And Lockheed has just signed a deal to acquire Sikorsky, maker of the world's most popular combat helicopter, the Black Hawk.

As if that weren't already enough, Lockheed Martin owns the franchise to build the world's only stealth fighter jet in active production today, the F-35 Lightning II, a plane program so huge that it could one day produce 50% of Lockheed Martin's revenues.

Underpromise, overdeliver
So there you have it, folks. We promised you "the" defense stock. But here we've gone and given you two bonus ideas. Boeing, Raytheon, and Lockheed Martin -- these are our top three defense plays for the decade to come.