Air and missile defense is one of the U.S. Army’s six modernization priorities. Based on current funding profiles, it is the number one priority, receiving about half the total funding the Army plans to spend on its priorities between 2020 and 2024.

The Army appears quite serious about improving its air and missile defense capabilities in the near-term and to do so wherever possible by exploiting available technologies and upgrading existing systems. This is an approach that has been characterized as an evolutionary revolution. Secretary of the Army Mark Esper explained this concept:

I don’t want to go (to a) white-sheet, long-term development program, years to determine requirements. We need to go with what we can assemble now in the next two-three years and then once we hit that readiness around the ‘22 time frame, start really putting money into procurement around ‘21, ‘22, ‘23 to start fielding by ’28.

Most immediately, the Army is upgrading its tactical air defense capabilities which were allowed to wither in the aftermath of the Cold War. It has distributed some of its limited inventory of the shoulder-fired Stinger system to forward deployed units.

The Army is conducting so-called heel-to-toe deployments of National Guard air defense battalions equipped with the Avenger Short-Range Air Missile Defense (SHORAD) system, essentially a Stinger missile launcher mounted on a Humvee. By exploiting technology already in advance development, the Army’s plans for an accelerated system may take a revolutionary turn with the addition of a laser weapon.

The Army is pursuing an evolutionary revolution with other portions of its air and missile defense portfolio. The combat-proven Patriot low altitude air and missile defense system is being upgraded with improved missiles and software. There is a program to provide Patriot with a new radar, the Sentinel, which will allow for 360-degree coverage and greater range.

Based on an urgent requirement from U.S. Forces Korea, the Army is working on linking Patriot with the Terminal High Altitude Area Defense (THAAD), both of which are deployed on the peninsula, so that the two can operate together in a layered defense. Integrating Patriot and THAAD is part of a future where any interceptor can employ any sensor, thereby greatly improving the overall effectiveness of the defense.

The Army is also seeking to invest in new capabilities for the early 2020s. Its major innovative program is the Integrated Battle Command System which is intended to connect all deployed air and missile defense systems. In addition, the Army is working on a Multi-Mission Launcher – a truck-mounted, multiple tube system that can fire different interceptors such as the AIM-9X Sidewinder missile, AGM-114 Hellfire missile and a new Miniature Hit-to-Kill missile.

But even as the Army moves aggressively to fill its capability gaps in air and missile defenses, our competitors are pursuing more advanced capabilities that could overwhelm or simply evade defenses the Army won’t even deploy for five years. According to the Vice Chairman of the Joint Chiefs of Staff, General Paul Selva, we have “lost our technical advantage in hypersonics.”

With all the money and attention the Army is devoting to getting new and improved air and missile defense capabilities into the field, why isn’t it moving aggressively to leverage THAAD, its most capable system? THAAD alone provides the theater commander with an air deployable, fast reaction defense against short and medium-range missiles.

It allows the Army to engage targets both within and outside the atmosphere. Integrated with the Patriot, THAAD gives the Army the ability to operate a multi-layer defense. In joint operations, THAAD covers the middle zone between the low-altitude Patriot and the high-altitude Standard Missile-3.

With the proper modifications, THAAD is uniquely capable of engaging advanced threats such as intercontinental ballistic missiles (ICBM), cruise missiles and hypersonic glide vehicles. In written testimony to the House Armed Services Strategic Forces Subcommittee in 2015, Admiral Cecil Haney, former commander of U.S. Strategic Command, proposed the THAAD-Extended Range (THAAD-ER) as a potential solution to these threats.

The THAAD-ER would provide a booster with greater range and a new kill vehicle with divert capability that would allow it to address maneuvering and high-speed threats. Further upgrades, such as a high maneuverable kill vehicle, would allow the Army to keep pace with advances in adversary hypersonic weapons.

Despite the identified evolution of the threat and the obvious growth potential for the THAAD, it is the one theater missile defense system without a funded block upgrade program. It is the only currently deployed missile defense system with a plausible growth path to address the advanced threat posed by hypersonic weapons and maneuvering warheads. THAAD, along with the Aegis Ashore defense system, could also be part of a highly-effective system to defend the Hawaiian Islands.

Part of the problem for THAAD is that it resides both in the Army and in the Missile Defense Agency (MDA). The Army mans and operates the seven existing THAAD batteries while MDA manages the program. Without the right demand signal from the Army, it is no surprise that MDA is not providing adequate funding for upgrades and testing.

There needs to be a serious well-funded effort to develop the THAAD follow-on, with an eye on the advanced threats. As part of this effort, THAAD needs to be tested against ICBM representative targets. Given the growing global demands for air and missile defenses, the Army needs to field at least two additional THAAD batteries, one of which should be deployed to defend Hawaii. Finally, the current program to integrate Patriot and THAAD needs to be extended to develop a launch-on-remote capability.

Daniel Gouré, Ph.D., is a vice president at the public-policy research think tank Lexington Institute. Goure has a background in the public sector and U.S. federal government, most recently serving as a member of the 2001 Department of Defense Transition Team. You can follow him on Twitter at @dgoure and the Lexington Institute @LexNextDC. Read his full bio here.