The Pentagon once replied to an 11-year-old who submitted his own missile designs with a brilliantly harsh letter.

Back in 1978, Canadian Reddit user 'schmal' sent the United States Department of Defence hand-drawn designs for ramjet-powered winged missiles with a nuclear warhead, a guidance system, and smaller missiles and machine guns. He never received his original designs back, but was delighted to receive a letter from the Department of the Navy evaluating them just over a month later.

The letter's author, named Robert, writing at the behest of the Chief of Naval Research, began courteously by noting the designs were "well drawn" - but then grew more critical. The reply explained why the Navy would be unable to adopt schmal's designs or their features, with a great deal of weaponry detail for a pre-teen.

The correspondence explained: "Generally, ramjet engines used for propulsion must reach super-sonic speeds before they are able to function properly. The missile, therefore, would require a rocket booster to achieve takeoff and the high speed needed. Additionally, you have shown relatively large wings which are not needed and would be inefficient at high supersonic or hypersonic speeds."

The letter referred schmal to enclosed information about current research into combined solid fuel/ramjet missiles, before going on to explain why the broad concept of his design of a missile carrying smaller missiles was "not considered to be new or novel".

"The Army is involved with antiballistic missiles that may be equipped with air defence guns, salvo guns that are aimed by radar and nuclear cannons," the letter continued, with further enclosed documents showing an existing similar delivery missile with submissiles.

Aside from those Redditors piling in to criticise young schmal's designs, most users loved the letter, with one saying: "I love how it started off nice and wholesome and then went into demolishing your ideas."

Another said: "Honestly I think it's fantastic the Navy did this and the right way to respond, educate and encourage." Others also credited the Navy for encouraging the boy to learn more about aeronautics principles and technical details of rockets.