Defense contractors occupy the top two spots on the list, with Honeywell (HON) (which admittedly has interests in several industries outside defense and aerospace) blowing past the competition with $553,999 in corporate PAC donations between January 1 and March 31 of this year. Northrop Grumman (NOC) follows at a distant second with $416,900 in contributions, while Boeing (BA) gave $304,500 and Raytheon (RTN) donated $238,500. General Electric (GE)—which also has a few interests in the defense industry—also contributed $304,000 via its corporate PAC.

The U.S. federal government is by far the biggest customer for most U.S. defense contractors, and it’s in no way unusual for these companies to spend millions lobbying Congress in a given year (collectively the defense industry spent nearly $128 million lobbying just last year). However, what is somewhat unusual is the industry’s dominance in PAC spending over other industries. With the 2016 defense budget currently under debate in Congress and major contract awards—like the $55 billion Long Range Strike Bomber program imminent—it’s a good time for defense contractors to have legislators in their corner.

All of the above mentioned defense contractors have multiple interests that influence their priorities, and future business with the U.S. government. But, while there’s no single program or spending measure dictating each contractor’s lobbying expenditures or PAC contributions, there are some major line items driving the uptick in contributions in 2015.

Raytheon: Rounding out the list of top 10 PAC contributors at number 10 is Raytheon. The defense company is probably best known outside the defense industry for its Patriot Missile System, which earned notoriety shooting down Scud missiles in Operation Desert Storm in the early 1990s. There’s no single program driving Raytheon’s business, since the company builds and/or supports a variety of missile and sensor systems for the U.S. military and its allies abroad. It’s also in the midst of updating the U.S. Army’s Patriot missile batteries, and an ongoing development program to enhance the Standard Missile 3 interceptor—a defensive system designed to knock other incoming missiles out of the sky—deployed by the U.S. Navy, and others.

Raytheon’s bottom line took something of a beating last year in the tough, budget-constrained U.S. defense market. However, multiple ongoing conflicts around the globe have helped Raytheon shop its wares abroad with relative success. The company has booked $5 billion in contracts for defensive missile systems since December alone, and it’s worth noting that exporting the kind of high-tech hardware Raytheon manufactures often requires U.S. government approval.

Boeing: As the world’s largest plane-maker, Boeing has plenty of reasons to make friends on Capitol Hill regardless of soon-to-be announced spending decisions, although a couple of developments over the past decade have left Boeing’s defense business in something of a bind. Boeing’s F-15 and F/A-18 fighter jet production lines are both slated to close by 2020 if no new orders emerge, with each of those aircraft being phased out in favor of the new F-35 Joint Strike Fighter (made by Lockheed Martin). This year the Navy submitted an unfunded request for more F/A-18 airframes that could extend Boeing’s fighter jet production into the next decade, but thus far Congress has not provided funds for that request.

Moreover, at the end of June, Congress allowed authorization for the Export-Import Bank to expire. Ex-Im, as the agency is often known previously guaranteed credit for foreign companies purchasing U.S. infrastructure-related equipment or, in Boeing’s case, airliners. Ex-Im disproportionately benefited Boeing—some even called it the “Boeing Bank”—since Ex-Im backstopped loans to airlines across the globe that in turn purchased Boeing’s aircraft. Without Ex-Im, Boeing says it could lose ground to rival Airbus. A vote to reauthorize Ex-Im is expected to hit the House floor in the days or weeks ahead, and Boeing could definitely benefit from its resurrection.

Then there’s the competition for the $55 billion Long Range Strike Bomber (LRS-B), the outcome of which could shake up both the combat jet industry at large and determine Boeing’s future.

Northrop Grumman: No one has more to lose in the Long Range Strike-Bomber competition than Northrop Grumman, which is far smaller than rivals Boeing or Lockheed Martin (LMT). The above mentioned companies have teamed up to compete against Northrop Grumman for what will likely be a $80 billion contract for the LRS-B program.

Northrop Grumman’s combat jet business—which makes the U.S. Air Force’s current fleet of B-2 stealth bombers—is all-in on LRS-B and failure to win the contract will likely force company leaders to make some tough decisions about the future of the firm. With no other major combat jet acquisition programs on the horizon for the next decade, a loss on LRS-B could force Northrop out of the lucrative defense business (Boeing faces a similar plight).

Contract decisions are (ostensibly) made on the merit of the aircraft design itself and not on purchased goodwill, but that hasn’t stopped each of Northrop’s competitors from waging intense lobbying campaigns in Washington D.C. over the past year. The fact that Northrop Grumman, with a market cap far smaller than either Boeing or Lockheed, is second only to Honeywell in PAC contributions says a lot about its current business plans.

Honeywell: Honeywell does business in a variety of sectors, so its place atop the list of PAC contributors for the first quarter can’t be chalked up purely to defense priorities. The company—which makes everything from aircraft components to thermostats—has, among many other things, several major long-term defense contracts hanging in the balance. The Obama Administration’s 2016 budget request asked for $51 million in funding for initial design work on a new engine to power thousands of Apache and Black Hawk helicopters into the 2020s, with another $720 million for development.

Honeywell and propulsion specialist Pratt & Whitney have teamed on an engine design and hired lobbyists to make the case for its engine over competitor GE’s. Contracts for initial design are expected in early 2016, with the ultimate winner of the contract announced in 2018.

Moving into the 2016 election cycle the public will be able to see just how much those PAC dollars paid off as Congress finalizes a fiscal 2016 defense budget and the Long Range Strike Bomber contract is awarded. New data on second quarter contributions should become available in the next couple of weeks, and it’s a fairly safe bet that defense industry dollars haven’t tapered significantly.