Which RPG models never made it into full production?

The RPG-3, RPG-4, RPG-5, and RPG-6 are models that were developed but did not proceed to full production. The RPG-3 was an early design that aimed to improve the launcher and warhead performance compared to its predecessors. RPG-4 was intended as a further evolution but did not meet the expectations for adoption. The RPG-5 and RPG-6 followed with various design changes and enhancements still not sufficient to warrant full production. Ultimately, these models did not reach the level of operational status and were eventually overshadowed by the more successful and widely used RPG-7.

In contrast, the RPG-2 was successfully mass-produced and widely used, which is why it is not included in the correct answer. Additionally, the RPG-1 was an early model, but it was quickly replaced and did not have longevity in production and use. The RPG-7, however, became one of the most iconic and utilized models, showcasing how production decisions were influenced by effectiveness and reliability in combat scenarios. Thus, the correct answer highlights the unsuccessful iterations in the RPG series before settling on the widely adopted designs.