... and to reply to the original post, it appears as if the use of the early rappier included training for war in the first European Military Academy, the Schola Militaris in Siegen. This was part of the Dutch military system which had a strong influence on Europe, and was adapted and improved upon by Swedish King Gustav II Adolf in his campaigns, when building the Swedish Empire in the 1600s .
Early on there was little difference in blade between a tapering arming sword and a swept-hilt rapier and both were obviously used in war. The more slender rapiers were also carried, at least by officers and it appears to me as if it is unclear to what extent they were used. They could certainly be used to thrust into the gaps of protection, just as can be seen in the Wallhausen images.
King Gustav II Adolf carried a rapier in his final battle in 1632 at Lützen, where his army succeeded in defeating Albrecht von Wallensteins army, despite the king being killed in the battle. The description of the injuries he sustained describes "several rapier thrusts" although it was a bullet that killed him.
It would seem likely that he also carried a main gauche, but I wouldn't think that there was much fighting done on the battle field with a dagger and sword in combination.
Also, pikes and firearms where much more important weapons in this time period, but for infantry at close range or on horseback the rappier appears to have been used even in the context of war.
Here is a nice article on rapiers and other swords:
http://www.armsarmour.com/a.pdf Unfortunately most of the text has been blurred, but the images are very pretty and enlightening. Also, keep in mind that the terminology used is that of museum curators and collectors and are as such often 19th century inventions.