The Challenger 2 TES Megatron, also known as the Challenger 2 OES (Operational Entry Standard), is a variant of the British Challenger 2 main battle tank designed for urban combat. In late 2004, Challenger 2 tanks were retrofitted with composite turret side armor and grilles on the rear sections of the hull and turret to protect against HEAT munitions. This armor configuration was designated Dorchester Level 2F (DL2F). The next modernization, which also aimed to strengthen the armor, took place in 2008. The tanks received composite armor side hull screens, and the NERA modules were replaced with reactive armor modules manufactured by the Israeli company Rafael Advanced Defense Systems Ltd. This variant of the Challenger 2 was designated TES (Theater Entry Standard).

In 2013, the Challenger 2 Megatron, also known as the TES, was unveiled to the public at the Bovington Museum. It is used to test new and potential future equipment for all Challenger 2 tanks in the British Army. The Megatron is frequently displayed at the Tankfest museum and regularly participates in various shows.

A special version of the Challenger 2 OES was introduced as part of the Senrai Maidens event in 2026. This tank differs from the other premium version due to its unique appearance, which is designed in the style of the character Emily. Emily embodies the stillness of a foggy morning, flawless discipline and quiet inevitability. Otherwise, the tanks are identical. The Challenger 2 OES is a welcome addition to the Challenger 2 TES in the research tree. It is equipped with additional armor packages that help against ATGMs. However, the tank's weight has increased to ~74 tons, significantly impacting its already subpar mobility.