First flight would have been in 1946. Work on the A9/A10 was prohibited after 1943 when all efforts were to be spent on perfection and production of the A4 as a weapon-in-being. Von Braun managed to continue some development and flight tests of the A9 under the cover name of A4b (i.e. a modification of the A4, and therefore a production-related project). In late 1944 work on the A9/A10 resumed under the code name Projekt Amerika, but no significant hardware development was possible after the last test of the A4b in January 1945.

The V-3 used Baron von Pirquet's concept of sequentially electrically activated angled side chambers to provide additional acceleration of the shell during its passage up the barrel of the gun. This allowed a muzzle velocity of over 1500 m/s. The projectiles of the smooth bore weapon used fins for stability, as would be the case with the Canadian Martlet series 25 years later.

Lyman and Haskell of the US Army had built an unsuccessful prototype of the concept in the 1880's. It was found that the expanding gases of the base charge moved well ahead of the shell and ignited the auxiliary charges before the shell passed them, actually slowing the shell down. But in 1941 an engineer Conders at Saar Roechling proposed the use of electrically-activated charges to eliminate the problem. A 20mm prototype was built at a test site at Misdroy (Miedzyzdroje), Poland and successfully demonstrated in April-May 1943. Hitler was persuaded that this could be a third terror weapon to supplement the V-1 and V-2. Overruling the German military, he ordered fifty of the guns to be built in concrete bunkers in France in order to bombard London. The first installation of five guns was to be built 165 km from London at Mimoyecques, near Calais, under Operation Wiese. The superguns were built at a fixed angle into a 30 m chalk hill, covered by a 5.2 m thick protective concrete dome. Each 140 m long cannon was capable of delivering a 150 mm / 140 kg shell on London.

The angled lateral combustion chambers were spaced every 3.65 m along the bore. The modular weapon could have the lateral chamber sections replaced as they wore out (they would burst after only a few firings).

Hundreds of slave workers began construction in September 1943 by sinking an initial tunnel 30 m below the hill's surface into the chalk. French Resistance informed the Allies of the new effort almost immediately. Bombing raids to destroy the site began two months later. However the bunker proved impervious to Allied bombs, even 5400 kg Tallboy penetrator weapons. The weapons were nearing completion when, on 6 July 1944, three Tallboys happened to make it though the gun shaft openings. They penetrated 30 m to the first level of the complex and exploded, killing dozens of workers. Work on the complex stopped at this point.

The Allies were unaware of this success and searched for new methods to destroy Mimoyecques and other German bunker sites. Under Project Aphrodite (USAAF) and Operation Anvil (USN) radio-controlled, television-guided B-17 or PB4Y (B-24) bombers crammed with ten tonnes of explosives were to be flown by a crew near to the target. The pilot and co-pilot would then bail out while an accompanying aircraft guided the missile to a precision strike. This approach was abandoned in August 1944 after a total lack of success and several crew fatalities (including Joseph P Kennedy, Jr, elder brother of the future president).

By the end of August the Germans completely abandoned the complex in the face of the advancing British forces. Two short-length (45 m long) V-3's were built at Antwerp and Luxembourg in support of the Ardennes offensive in December 1944. These were found to be unreliable and only a few shots were fired without known effect. The British dynamited the Mimoyecques complex on 9 May 1945.

Test pilot V P Fedorov was towed to 2600 m and cast off at 80 km/hr. The rocket then fired and accelerated the aircraft to 140 m/s and 2900 m altitude. The RP-318 flew nine times before the war ended the work.

Studies for a copy of the Me-163B rocket fighter were already undertaken by OKB MiG in 1944. Post-war Soviet technical teams discovered the more advanced Ju-248 (Me-263) design and the decision was made that MiG would copy this design. The first airframe, Zh-1, began glider tests in December 1946. The Zh-2, rocket-powered with a dual thrust engine first flew in March 1947. The I-270 was abandoned after the Zh-2 was written off after a hard landing in spring 1947.