Would the Allies still have been victorious?

Sir Harry Hinsley is not only a WW2 historian, but also worked at Bletchley Park during the war....which gives him a pretty good perspective on the whole issue. He thinks Ultra shortened the war by two, but more probably four years. I would tend to agree. Reading WW2 history these days (compared to 20 years ago when we didn't know much about Ultra as it was still secret) Ultra intel was used in pivotal campaigns all through the European theatre. North Africa, Italy, U boat warfare in the Atlantic, Normandy, and given to (and acquired by a spy of) the Russians to their advantage at Stalingrad and Kursk.

Very probably without Ultra, the Brits may not been able to evacuate Greece, Rommel would have won in North Africa and with air Luftwaffe superiority would have dominated the Mediterranean. The Germans would have taken Malta. The Germans may very well have won at Kursk. U boats destruction of shipping would not only have continued, but would have increased as more U boats were put into action, though British anti U boat defences may have eventually curtailed this. Troops that were used in North Africa and in Italy at that point in the war, could have been put into the Eastern Front, which once again could of made the difference to Stalingrad and Kursk. You could also speculate that with the Germans doing well in 1942/43, that Italy may have stayed with them.

The Axis powers would have stepped up V2 production, though its hard to say what affect an elongated V2 campaign against the UK would have had. With another couple of years, the Germans would have had more time to develop jet technology, with a theoretically better developed and deployed ME 262.

The US, however still would have developed the Atom bomb, and its doubtful a Nazi Atom bomb counter would have been developed even with the Third Reich staying in power until 1949.

 

As we don't know how much shipping was saved by Ultra and how much UBoats were lost by Ultra,it's all (IMHO useless) speculation.
Btw:as Hinsley worked in Bletchey Park,one can't say he is an impartial historian .Of course,he will say that Ultra was decisive .
And,saying that because of Ultra ,the British could evacuate Greece,the British won in NA,the Germans could win in Stalingrad and Kursk,etc:this all is unproved speculation,and,IMHO,jingoistic blahblah :it is saying ,without Ultra (=Britain)Germany would have won in the west and against the SU It is also not knowing that Stalingrad and Kursk were battles of minor importance,and not knowing,that ,after september 1941,Germany had lost all chances to win in the east ..