FORT WORTH, Texas — America's most expensive weapons system ever built is on track for "initial combat use" by September 2016.

Business Insider recently toured Lockheed Martin's massive production facility in Fort Worth, Texas, where the three F-35 Lightning II variant aircraft are designed and manufactured.

The $400 billion and counting F-35 program has so far delivered 140 of the anticipated 2,443 jets to the US Department of Defense and five aircraft to foreign military buyers.

Here is a look at the unique capabilities of the F-35 variant aircraft:

The lightest of the jets is the F-35A:

The F-35B is in the middle at 14.3 feet tall and weighs 32,300 pounds.

The F-35C is the tallest and the heaviest:

Lockheed Martin/Amanda Macias/Business Insider

The F-35A and F-35B have the same wingspan and nearly the same length:

F-35A Lockheed Martin/Amanda Macias/Business Insider

Designed for the Navy, the F-35C features longer wings to create drag for the jet to slowly land on aircraft carriers:

The F-35C has another unique wing design:

The F-35A is the only variant that has an internal gun; aside from that, the jets have similar designs:

The F-35A conventional takeoff and landing (CTOL) variant’s advanced sensor package is designed to gather and distribute more information than any fighter in history. Lockheed Martin/Amanda Macias/Business Insider

All three variants are coated with a special material to avoid radar:

The F-35 jets have serious firepower:

Lockheed Martin/Amanda Macias/Business Insider

Lockheed Martin/Amanda Macias/Business Insider Lockheed Martin/Amanda Macias/Business Insider

The F-35C carries 19,750 pounds of fuel, the most fuel of the variant aircraft. All jets have the capability to be refueled in air:

The F-35A is refueled differently: