We tested sub kilo newton devices because we want to use them in our short range tactical ballistic missiles. We developed Prahaar short range tactical missile system exactly for delivering such sub kilo newton nuclear devices.
Prithvi 1(150km) and prithvi 2 (350km) are liquid fueled missiles. Prithvi 1 carries a payload of 1000 Kgs, while Prithvi 2 carries a payload of 500 kgs. Prithvi 1 is an army version, prithvi 2 is an airforce version and Prithvi 3 (350km), which is a solid fueled missile is a naval version with a payload capacity of 1000Kgs. Liquid fuelled missiles have a higher reaction time to fill the missile with fuel and are less preferred than the solid fuelled ones that can be launched within 2-3 minutes.
The relationship between payload weight and energy yield can be seen in the attached screen shot. (Courtesy:
https://en.wikipedia.org/wiki/Nuclear_weapon_yield)
A nuclear war head that weighs upto 700 kgs approx can be used as a low weight, low yield tactical weapon (yield below 1kT). In order to develop a short range, highly accurate and low altitude, supersonic, solid fuelled ballistic missile that is capable of being used as a tactical and a strategic nuclear weapon, we developed Prahaar missile system, which is between the Pinaka system and Prithvi.
Prahaar is a supersonic (Mach 2+) solid fueled SHORT RANGE (150km) with lower flight altitude(35 km), that can be used for both strategic and tactical targets. It can carry a conventional or a nuclear warhead upto 200KGs that can generate a sub kT yield, if we have mastered the art of making such small war nuclear heads. (I am inclined to believe that we have, when we tested the sub kT devices). Both the army and the Airforce will be using Prahaar. In all probability, they will and can use Prahaar as our tactical as well as strategic missile with sub kT nuclear warheads, if they choose to.
https://en.wikipedia.org/wiki/Prahaar_(missile)