US President Barack Obama tested a new prototype Tuesday for his commander-in-chief's arsenal -- a high-powered marshmallow gun that sent a tasty missile screaming through the White House.

Watched over by a brooding portrait of his hero Abraham Lincoln, the US president fired the launcher and marveled at other inventions on display at a White House youth Science Fair.

Obama gleefully examined a "Skype on wheels" robot that allows elderly people use the Internet to talk to far away relatives and a unique sugar sachet that dissolves in a cup of coffee, to avoid creating garbage. But he could not resist the marshmallow launcher.

"The Secret Service is going to be mad at me about this," Obama said, before energetically pumping a compressor and shooting the marshmallow gun, invented by 14-year-old Joey Hudy.

Obama watched open-mouthed as the candy shot across the room before crashing into the wall near the entrance to the Red Room, an elegant state parlor which stuffed with rare 19th century French furniture.

All the fun of the science fair had a serious purpose. Obama wanted to highlight the importance he places on innovation, science and education -- which will be reflected in his budget to be unveiled next week.