Even a country the size of the United States was suffering a manpower shortage in 1943, in the middle of the Second World Two. It was a 'double whammy' effect - men were required in huge numbers for the army, navy and air force yet at the same time it required many more in the armament industries. Typewriter firms built rifles, car makers turned out tanks. 
The solution was to encourage women to fill the labour shortage, and when the SS Jeremiah O'Brien was built, in mid 1943, a third of the workforce were women. If the thought of a woman as a welder, a riveter, crane operator or labourer sounds a bit unusual now, it must have been shocking in the 1940s.
To try to persuade women to apply for jobs in the 'manual' trades, they came up with the 'Rosie the Riveter' campaign with the slogan "We can do it" (Rosie looks a bit butch in the poster - perhaps taking a cue from the Soviet revolutionary posters of the 1930s).
