The Vietnam War

Another well-publicized example of steganography happened during the height of the Vietnam War. Commander Jeremiah Denton was a naval pilot who had been shot down and captured. At one point he was taken by the North Vietnamese and paraded around in front of the media as part of a propaganda event. Knowing that he was under the proverbial microscope and unable to say anything openly critical about his captors he blinked his eyes in Morse code, spelling out T-O-R-T-U-R-E, as he spoke to the media.

During the Vietnam era, there were instances where captured members of the U.S. Armed Forces would use various hand gestures during photo ops; often, these gestures were airbrushed out by the media. Prisoners of the infamous Hanoi Hilton used a "tap code" to communicate with each other. The code was based on a five-by-five matrix, with each letter being assigned a tap sequence based on this matrix. Spaces (pauses) between characters were twice as long as the spaces in that letter's code (Table 3.1).

Table 3.1: The 5 5 Tap Code Used by Prisoners in Vietnam

	1	2	3	4	5
1	A . .	B . ..	C, K . …	D . ….	E . …..
2	F .. .	G .. ..	H .. …	I .. ….	J .. …..
3	L … .	M … ..	N … …	O … ….	P … …..
4	Q …. .	R …. ..	S …. …	T …. ….	U …. …..
5	V ….. .	W ….. ..	X ….. …	Y ….. ….	Z ….. …..