Rheinmetall-Borsig started work on a mobile ramp launcher for the V-1 missile in '42, long before the German fixed ramps were built. The Startrampe (Start Ramp) was equipped with a Startwagen (rocket sled that ran along three slits in the ramp and was equipped with 4x Schmidding 109-533 solid fuel rocket boosters each producing 2650 lb st). The V-1 sat atop it and the ramp was angled 6 degrees. When fired the sled accelerated until the brake stopped it at the edge, propelling the V-1 into the air at 242 mph for the pulsejet to operate. Although promising and mobile, the Luftwaffe went with the alternate Walter rocket piston system. The ramp was longer and the V-1 was fed compressed air to operate the pulsejet when idle. This reduced launch speed to 186 mph. When the V-1 became operational in 1944 and then bombed by the Allies, the mobile launcher idea was still rejected b/c the Germans prefabricated ramp components for ease of reconstruction. Unlike the V-2 with its mobile lauch ramp, single V-1 launches were impractical given that the majority were shot down upon approach to Britain. The Luftwaffe simply had them adapted for air-drop by He-111 aircraft. As the war was ending, on Misdroy new ramps were constructed aimed North at Sweden with the Henschel V-4 which was ramjet powered and fitted with solid rocket boosters...

He-111 with tucked V-1: http://tanks45.tripod.com/Jets45/Histories/He111/He111-V1.jpg