“Did they mean RAP (Rocket Assisted Projectile) round? I don’t think a RAM-jet is feasible for artillery.”
Hybrid systems - part rocket, part ramjet - have been in routine use for decades in guided missile systems. Auxiliary pure rockets boost the missile airframe to an airspeed high enough to keep the ramjet operating; then it takes over and powers the missile airframe the rest of the way to the target.
The advantages of a ramjet over a gas-turbine jet are simplicity, cost, and weight; the disadvantages are that a fairly constant speed must be maintained; so a ramjet cannot operate in as many different flight regimes as a turbojet.
One advantage of a ramjet over a pure rocket is smaller size/weight for a given payload, speed, and range; the ramjet uses external air and does not need to tote its own oxidizer. One disadvantage: external air supply is crucial. Rockets do tote their own oxidizer and don’t need air to operate.
A question not brought up in the article: can a ramjet be fitted into a projectile small enough to be fired from a gun barrel? Turbojets are made small enough these days, to fit into radio-controlled model aircraft; perhaps ramjets can be downsized the same way.
SJSAMPLE is quite right to be concerned about feasibility.
Yeah, but I was an artillerymen for 16 years and the only system I used that came even close to RAM-jet speeds was the Lance (MGM-52) missile, which would do mach 3 by the time it cleared the launcher. With 8”, 155mm and 105mm, I could see the rounds leaving the tubes and sometimes track them downrange. All of the RAM-jet tests I’ve seen were after the missile was accelerated to Mach5 with a SRB. I just can’t imagine a RAM-jet in a 155mm sized projectile or, really, any tube artillery projectile.