AH-1 'Cobra' launches an AIM-9M 'Sidewinder' missile.

When helicopters entered widespread military use during the early 1950s they were almost exclusively specialised for observation, liaison and transport roles.
The advent of helicopters large enough to lift a squad of troops opened up a range of new possibilities, and initiated the evolutionary path for helicopters as platforms for sensors, weapons or both. Helicopters were used to support land forces, and helicopter types were developed for naval applications.
Even today, while basic airframe designs are shared between land based and naval helicopter variants the avionics/sensor suites and weapons packages tend to be fundamentally different, reflecting differences between land and maritime warfare.
The evolution of helicopter ISR (Intelligence Surveillance Reconnaissance) capabilities reflects several threads of evolution.