Former officer Charles Heyman, who edits a yearbook on British forces, said the prince's words may raise the already high threat level against him.
"The royal family are all targets, and he now probably becomes the prime target, royal family-wise," Heyman said. "But he can live with that. He's a soldier, he knows what he's doing."
Heyman said it was commendable that Harry had undertaken such a dangerous and demanding military job.
"By and large, the world's elite make sure their sons and daughters go nowhere near the firing line. So it brings credit to the royal family, and it's good for army morale, that Harry's not sitting back in London saying, 'Well done, boys!'" he said.
Heyman said as an Apache gunner, Harry would have opened fire when directed to do so by a ground controller who would most likely have been under enemy fire. The prince typically would have been firing at Taliban forces in bunkers or protected in some way, not at troops out in the open, said the former officer.
"They would have been opening fire to relieve pressure on the ground, maybe even to rescue people on the ground," Heyman explained. "If he was using machine guns, there is no way he could say categorically he destroyed the target. But if he was using the Hellfire missiles against a bunker, he would be able to say categorically that he destroyed the target."
If there's a large explosion and no more enemy fire from the target area, the gunner can be "pretty sure" the enemy has been killed, Heyman said.
Col. Richard Kemp, a former British commander in Afghanistan, said the fevered press response to Harry's words reflected a certain naivety about the realities of war.