Depends on what you call “major”. https://en.wikipedia.org/wiki/V-2_rocket#Operational_history https://en.wikipedia.org/wiki/V-2_rocket#Operational_history: “F

Depends on what you call “major”. https://en.wikipedia.org/wiki/V-2_rocket#Operational_history https://en.wikipedia.org/wiki/V-2_rocket#Operational_history: “From a field near the village of Serooskerke, five V-2s were launched on 15 and 16 September, with one more successful and one failed launch on the 18th“ That must mean they launched at least 3 on either the 15th or the 16th. That page also says “Beginning in September 1944, more than 3,000 V-2s were launched” and “The final two rockets exploded on 27 March 1945”, so that’s over 3,000 in at most 208 days, so there must have been days there were at least 14 “launches in a single day by the same entity”. I suspect the actual top number is a lot higher. If you think that’s borderline “a single entity”, there’s “After the US Army captured the Ludendorff Bridge during the Battle of Remagen on 7 March 1945, the Germans were desperate to destroy it. On 17 March 1945, they fired eleven V-2 missiles at the bridge”