Was it really impossible for Lenin to return to Russia without German consent? Lenin's own alleged ideas about how to do so were all crazy. For example, he would pretend to be a deaf-and-dumb Swede while taking the train across Germany. Krupskaya persuaded him that he would inevitably give himself away by muttering curses against the Mensheviks in his sleep.
http://www.marxists.org/archive/krupskaya/works/rol/rol21.htm (According to Adam Ulam, *The Bolsheviks,* pp. 326-7, "Hanecki, Lenin's agent in Stockholm, and a very inept liar, gives the most grotesque version: Lenin wrote him in March asking for passports of two Swedes who looked like him and Zinoviev. He and his inseparable lieutenant were going to skip through Germany as *two* deaf and dumb Swedes..."
http://books.google.com/books?id=TdCK1WkconkC&pg=PA326)
It seems to be assumed that because Lenin had so violently denounced the Allied war effort, there is no way that he could have returned to Russia (legally, at least) through Allied territory. [1] But is this necessarily true? Consider the case of Trotsky. After leaving New York, he was indeed detained by British authorities in Halifax because of his anti-war views. Yet the British did ultimately decide to release him and let him return to Russia at the request of the Provisional Government, which was under heavy pressure from the Petrograd Soviet. (The position of the Soviet--reluctantly adopted by the PG--was that *all* political exiles, regardless of their stance on the war, had to be allowed to return.) So while the French government might similarly detain Lenin if he tried to travel through French territory, might it not also have decided that it had no choice but to release him? (Admittedly, Lenin had gone even further than Trotsky, actually calling for the defeat of Russia.) Of course, there would still remain the danger of Germam submarines, but if Trotsky could brave that danger, presumably Lenin could if necessary.
[1] One of the few people to question this assumption is Stefan T. Possony in *Lenin: The Compulsive Revolutionary*:
"Unlike other revolutionaries he did not go to the British and French consulates. He asked Safarov to lend him his passport so that he could travel through France under a false name. Yet Safarov had been disseminating defeatist propaganda to the French army. With his passport Lenin would have met with more trouble with the French authorities than if he had been traveling under his own name; preparations for the trip were discontinued.
"But presently, Lenin's old enemy, Martov, suggested at a meeting at Geneva with Bolsheviks on March 19, that the revolutionaries be permitted to pass through Germany in exchange for Austrian and German prisoners of war...This proposal was contingent upon approval by the Petrograd government.
"Martov made the unfounded assumption that France and Britain would deny passage. It was not unreasonable to expect difficulties, but the proper course of action would have been to request instructions and diplomatic and consular assistance from Petrograd. Yet Lenin and his temporary allies of Menshevik loyalty did not even consider applying for passage through allied territory, despite the fact that many Russian emigres were returning home via the West, usually in allied ships.
"The Bolsheviks and international Mensheviks, as well as the left Social Revolutionaries, the Jewish Bund, Polish socialists, and other defeatist groups had had dealings with the Central Powers...The key men in these groups, uncertain as to what extent their secret contacts had been detected, did not wish to risk indictment for espionage. The German legation believed, however, that the revolutionaries feared the sea voyage with its peril of submarine attack..."
http://www.yamaguchy.com/library/pearson/lenin_36.html