Early games used interactive electronic devices with various display formats. The earliest example is from 1947—a "Cathode ray tube Amusement Device" was filed for a patent on 25 January 1947, by Thomas T. Goldsmith Jr. and Estle Ray Mann, and issued on 14 December 1948, as U.S. Patent 2455992. Inspired by radar display technology, it consisted of an analog device that allowed a user to control a vector-drawn dot on the screen to simulate a missile being fired at targets, which were drawings fixed to the screen. Other early examples include: Christopher Strachey's Draughts game, the Nimrod computer at the 1951 Festival of Britain; OXO a tic-tac-toe Computer game by Alexander S. Douglas for the EDSAC in 1952; Tennis for Two, an electronic interactive game engineered by William Higinbotham in 1958; and Spacewar!, written by MIT students Martin Graetz, Steve Russell, and Wayne Wiitanen's on a DEC PDP-1 computer in 1961. Each game used different means of display: NIMROD used a panel of lights to play the game of Nim, OXO used a graphical display to play tic-tac-toe Tennis for Two used an oscilloscope to display a side view of a tennis court, and Spacewar! used the DEC PDP-1's vector display to have two spaceships battle each other.