The Tactical High-Energy Laser, or THEL, is a laser developed for military use, also known as the Nautilus laser system. The mobile version is the Mobile Tactical High-Energy Laser, or MTHEL.

The cooperative Tactical High Energy Laser (THEL) Demonstrator ACTD was designed and built by the Israeli government on July 18, 1996.The project was later funded by the United States. The THEL is a high-energy laser weapon system that uses proven laser beam generation technologies, proven beam-pointing technologies, and existing sensors and communication networks to provide a new active defense capability in counter air missions. The goal of THEL is to provide a different solution than other systems or technologies for the acquisition and close-in engagement problems associated with short- to medium-range threats, thereby significantly enhancing coverage of combat forces and theater-level assets. The THEL low cost-per-kill (about $3,000 per kill) could also provide a cost-effective defense against low-cost air threats. It features up to 60 shots without reloading and if it meets design goals, a probability of kill of nearly 100% at a range of 5 km.