Which of the following is NOT a variant of the F-35?

The F-35D is not a recognized variant of the F-35 family. The F-35 program includes three primary variants: the F-35A, which is designed for conventional takeoff and landing; the F-35B, which features short takeoff and vertical landing capabilities; and the F-35C, which is tailored for carrier operations and has larger wings and strengthened landing gear for effective performance on aircraft carriers. Each of these variants serves distinct operational needs within the military services of different countries.

In contrast, F-35D does not exist among the official designations pertaining to the F-35 program. This clearly distinguishes it from the acknowledged variants that fulfill specific roles and requirements in modern warfare.