To understand Trotsky’s Proletarian Military Policy for WWII in the democratic imperialist states, it is necessary to use the logic of materialist dialectics. WWII was the continuation of WWI but not a repetition of it. It was different because of the Soviet Union that was not a capitalist state and because some imperialist states had a democratic form that had to be considered for tactical reasons, while in content, both imperialist camps were the main enemy.
The Proletarian Military Policy’s aim was to turn the American working class’s desire to fight fascism into a revolutionary perspective of overthrowing its "own" imperialist state. The essence of the proletarian military policy was a call for trade-union control of the compulsory military training being instituted by the state. Of course, the American ruling class would oppose such a policy, but it could appeal to the working class.
Unfortunately, after Trotsky was murdered by a Stalinist agent, the SWP tilted the policy in the direction of reformism when they explained during their trial that Nazi Germany is the enemy, forgetting that in each imperial state the main enemy is at home. This caused later groups like the ICL to reject Trotsky’s correct tactic altogether.
In the war of 1948 between Israel, the Palestinians and the Arab states, it was necessary to oppose the Zionist state and use the tactic of revolutionary defense for the Arab armies, even though the high officers of the Jordanian legion, for example, were British. The reason was that the essence of the war by Israel was to expel the Palestinian masses and the Arab states entered the war under the pressure of the Arab masses that felt solidarity with the Palestinians suffering from brutal massacres.
In May 1948 the organ of the Fourth International published the mistaken position of Trotskyists in Palestine led by Ygael Gluckstein, known later as Tony Cliff, who could not adopt a revolutionary position in support of the Palestinians.
The group Revolutionary Communist League wrote:
"The two camps today mobilize the masses under the mask of "self-defense." "We have been attacked, let us defend ourselves!" – say the Zionists. "Let us ward off the danger of a Jewish conquest!" – declares the Arab Higher Committee. Where does the truth lie?
War is the continuation of politics by other means. The war led by the Arab feudalists is but the continuation of their reactionary war on the worker and the fellah who are striving to shake off oppression and exploitation. For the feudal effendis "Salvation of Palestine" means safeguarding their revenues at the expense of the fellahin, maintaining their autocratic rule in town and country, smashing the proletarian organizations and international class solidarity.
The war waged by the Zionists is the continuation of their expansionist policy based on discrimination between the two peoples: they defend kibbush avoda (ousting of Arab labor), kibbush adama (ousting of the fellah), boycott of Arab goods, "Hebrew rule." The military conflict is a direct result of the policy of the Zionist conquerors.
This war can on neither side be said to bear a progressive character. The war does not release progressive forces or do away with social and economic obstacles in the path of development of the two nations. Quite the opposite is true. It is apt to obscure the class antagonism and to open the gate for nationalist excesses. It weakens the proletariat and strengthens imperialism in both camps." 
This position has three main mistakes. First of all, the Arab semi-colonies were not feudal as feudalism did not exist in the Middle East. The mode of production under the Ottoman was the Asian mode of Production. In 1948 the Arab states were underdeveloped capitalist colonies or semi-colonies, super exploited by the imperialists.
Secondly, the essence of the 1948 war was the Zionists’ ethnic cleansing of Palestine, not a war against British imperialism. A war similar to the American white colonialist settlers against the native nations.
Thirdly, a victory in a war of semi-colonies against settler colonialists in the epoch of imperialism would have been a victory against the main enemy of the working class - the imperialists and would encourage other workers and oppressed people to fight against imperialism. 
The British government supported the Zionists in the war. In April 1948, British forces, which had hitherto acted as a buffer between Jews and Arabs forces in Haifa, the largest port town, announced to the Jewish authorities there that they would be withdrawing. This sent a green light to proceed with the city’s ‘de-Arabisation’, which involved expelling its 75,000 Palestinian residents, and is described by the Israeli historian Ilan Pappe as “one of the most shameful chapters in the history of the British empire in the Middle East”.
The same fate befell the city of Jaffa, which was taken in May 1948 after a three-week long siege by Israeli forces, who succeeded in expelling the entire population of 50,000 with the ‘help’ of British mediation. In parts of Jerusalem, the British even disarmed the few Arab residents defending themselves against Jewish attacks on their neighborhoods. The British also aided Israel’s annexation of Palestine in other ways, such as handing over land ownership deeds for villages, which provided vital information to aid the depopulation process. 
The Jordanian legion, in spite of the fact that it was commanded by British officers, and in spite the secret deal of King Abdulla with the Zionists of dividing the lands that according to the partition plan was supposed to be an independent Palestinian state, fought against Israel because of the pressures of the Arab masses, including Arab officers of the legion, who felt solidarity with the Palestinians. For this reason the policy of revolutionary defense of the Arab armies was the only correct revolutionary position.
The victory of Israel in the war of 1948 set back the economy of the Arab states and strengthened the control of British and American imperialists in the region. It also set back the workers struggle in the Arab states.
On this the Trotskyist Gabriel Baer wrote in 1949:
"However, the creation of the State of Israel as a diversion for the Arab masses of the Middle East from the anti-imperialist struggle, was not the only gain for Anglo-American imperialism from the war and the new balance of power. An important by-product of last year’s events was the exhaustion of resources and reserves of almost all the Middle Eastern governments. Benefiting from the war-time prosperity of World War II, the Arab bourgeoisie all over the Middle East and especially in Egypt gained strength and resources, considerably improving their bargaining position vis-a-vis British imperialism.
… It would be futile to deny that the period of the last year, from May 1948 to May 1949, has been a period of stagnation of the labor movement in the Arab East, except perhaps for some countries on the fringe of the Arab states like the Sudan (where strong trade unions came into being and took part in the political struggle of the Sudanese anti-imperialist movement.” 
Thus the Israeli victory in the war of 1948 set back the forces of production in the Arab states and the struggle of the working class and the oppressed. For this reason it was necessary to defend the armies of the semi-colonies regardless of the reactionary leadership of the Arabs, without giving them political support.
The right centrist of the CWI and the IMT take a similar wrong position to the Trotskyists in Palestine in 1948. They see the Israeli working class as the key for a socialist transformation of Palestine and they call for two "socialist states". This position reflects their pro Zionist politics.
 See on this e.g. Yossi Schwartz: Israel’s Six-Day War of 1967. On the Character of the War, the Marxist Analysis and the Position of the Israeli Left, in: Revolutionary Communism No. 12, July/August 2013, http://www.thecommunists.net/theory/israel-s-war-of-1967/