"I believe today that my conduct is in accordance with the will of the Almighty Creator."

- Adolf Hitler in "Mein Kampf", Vol. 1 Chapter 2

Adolf Hitler was quoted as late as in the year 1943 by General Gerhard Engel as saying in a private discussion: “I am now as before a Catholic and will always remain so." On the other hand, there is a league of Christian apologetic's who claim that Hitler was always a "secret atheist". They also claim that his atheism grew in secret, and he ended up a Stark Naked Atheist, but he just did not ever admit this alleged secret atheism to anyone.

However, they are saying these things because they are trying to hide away from view the darkest family secret of Christianity. A sad fact of history is that all the major Christian denominations in Germany embraced Nazism and Adolf Hitler openly. They did often this until his downfall. Also, all too many of the Christian organizations abroad saw Hitler as a savior or Western civilization against the godless Communism. One of them was the papacy of Rome.
This hideous failing of judgment has been carefully blotted out of history that is taught to us. Commonly ever mentioned are the likes of Christian opposition men Martin Niemöller and Dietrich Bonhoeffer, who were later sent to concentration camps. The fact that what these men really opposed was the official Nazi line of their very own official Christian church is never really mentioned anywhere.

 The SA not only instigated street violence against Jews, Communists and Socialists, it also enforced boycotts against Jewish-owned business, such as this one in Berlin in 1933. - Wikipedia

In his study The Holy Reich, the historian Richard Steigmann-Gall writes:

"The insistence that Nazism was an anti-Christian movement has been one of the most enduring truisms of the past fifty years. ... Exploring the possibility that many Nazis regarded themselves as Christian would have decisively undermined the myths of the Cold War and the regeneration of the German nation. ... That Nazism as the world-historical metaphor for human evil and wickedness should in some way have been related to Christianity can therefore be regarded by many only as unthinkable."

The Christian apologetics very commonly persist in their claims, even when they are presented with formidable new evidence saying that they are wrong. As true believers, they just brush away all new evidence as lies. They just want to believe in their invented inner states of mind for Adolf Hitler that are not, in fact, based on any kind of real evidence.
The hidden, secret inner convictions of Adolf Hitler will of course never be known. However, we know very well what Nazis did in the real world. We know that all humanistic and atheistic organizations were strictly forbidden in Germany in the very first year of Nazi rule, that is in the year of 1933. On the other hand, no established official Christian organization was never even harassed during his whole reign because of religious reasons.

In a speech, in the year 1933 Hitler proudly declared:

"We have… undertaken the fight against the atheistic movement, and that not merely with a few theoretical declarations: we have stamped it out."

The prewar great freethinking movement of Germany was crushed without leaving a trace, when church bells were rung to rejoice the victories of the Fatherland during the whole of the reign of the Nazis. Among the chairmen of German Freethinkers League was Max Sievers, who was beheaded at the guillotine by the Nazis in 1944.
The German Freethinkers League had by 1930 a membership numbering around 500 000. The League was closed down, however, in the spring of 1933 when Hitler outlawed all atheistic and freethinking groups in Germany. 'Freethinkers Hall', the national headquarters of the League, was then converted to a bureau advising the public on church matters.

The only true Christian opposition ever to materialize against Hitler was the Confessing Church. It was formed by a few brave lonely souls. They did fight against the official Nazi line of the official German Protestant churches. Its leaders like Martin Niemöller and Dietrich Bonhoeffer were later sent to concentration camps. They formed, however, just a tiny splinter group with around 12 000 members according to some sources, when the official Protestant churches that supported Nazis had 45 million members.
It is true that also some individual Christians were targeted and persecuted, but only if they were in real opposition to the system. One has also to bear in mind that similarly targeted were all other individuals of any creed who caused any similar trouble to the system. A sad fact of life is that the official Christian institutions of Germany never caused such trouble.

One of the main assets of the Christian apologists has been to present those Nazis who advocated a twisted form of ancient German mythology as some kind of atheists. However, these people were theists, who just chose to switch the Christian god to the old Germanic ones. A person advocating even an old god is not an atheist. These beliefs did, however, never gain the upper hand even in the Nazi Party, and both the Nazi Party and the Nazi Germany remained overwhelmingly Christian to the bitter end.
It is also good to remember that Nazis did persecute Jews because they had a strong belief in the inherent inferiority of the Jewish "race". This belief did not rest on any kind of true scientific basis. It rested on their willingness to accept unproven strong beliefs and unsupported strong claims as a basis for the real world actions.

In the real world, Hitler also made an amiable agreement of power sharing with the Catholic Church or the famous Reichskonkordat http://en.wikipedia.org/wiki/Reichskonkordat with the papacy as one of his official acts as the Chancellor of Germany. The Nazi relations with papacy were admittedly strained at times, as papacy was seen as a threat to the absolute control of the party. These issues were, however, always resolved.
The Catholic Church did never officially oppose the Nazi government of Germany and the Nazis never attacked the official institutions of Catholic Church in Germany. Of course, also Catholic individuals who opposed Nazism was persecuted, as were all other known opponents of the regime.

Hitler had extremely amiable relationships with all of the major German protestant Churches of his day. They just could not think enough new things to please Hitler. The Protestant Reich Church or the Reichskirche was formed in 1933 by merging 28 regional churches into a unified state church. This espoused a single doctrine that was compatible with National Socialism.
There was also a powerful and openly Nazi Protestant group called the Deutsche Christen. See http://en.wikipedia.org/wiki/German_Christians

I would, however, never claim that Hitler was a "true Christian" the more than Winston Churchill was. Churchill was, in fact, in private even more skeptic in religious matters than Hitler was. At least in the "Churchill: A Life" by Martin Gilbert, Winston Churchill is quoted as calling religion "a delicious narcotic" and indicating people shouldn't be too concerned with the afterlife. Hitler never uttered such things in public.
I know that there is an old tradition in Christian circles in claiming that if Christians do commit crimes, they have simply renounced Christianity for the duration of committing those crimes, at least. Building on this base it is easy to say that Hitler was not a Christian because he did non-Christian things.
It is also clear that he did not do the terrible things he did to promote Christianity either. He did them because he had invented a new kind of ultra-nationalistic creed. In the end, he only used also Christianity to further this ideology.

However, we have no kind of evidence for that he would have done the things he did because of some kind of "hidden atheism" either. Hitler simply used a religion that propagates total submission to authority as an extremely handy tool for achieving his own ends, as well as Winston Churchill was very apt on using religious sentiments to further his own goals, even if he did not personally have much faith in religion.
However, this does not make Hitler an "hidden atheist". This is a thing that some Christians still stubbornly claim just because it makes them feel better and what is most important; it helps to hide the terrible secret of Christian Nazism.

Here are some original quotes by Mr. Adolf Hitler himself on the issue of religion:

"Even today I am not ashamed to say that, overpowered by stormy enthusiasm, I fell down on my knees and thanked Heaven from an overflowing heart for granting me the good fortune of being permitted to live at this time."

- Adolf Hitler, Mein Kampf, Vol. 1 Chapter 5

"Once again the songs of the fatherland roared to the heavens along the endless marching columns, and for the last time the Lord's grace smiled on His ungrateful children."

- Adolf Hitler reflecting on World War I, Mein Kampf, Vol. 1, Chapter 7

"What we have to fight for is the necessary security for the existence and increase of our race and people, the subsistence of its children and maintenance of our racial stock unmixed, the freedom and independence of the Fatherland; so that our people may be enabled to fulfill the mission assigned to it by the Creator."

- Adolf Hitler, Mein Kampf, Vol. 1 Chapter 8

"But if out of smugness, or even cowardice, this battle is not fought to its end, then take a look at the peoples five hundred years from now. I think you will find but few images of God, unless you want to profane the Almighty."

- Adolf Hitler, Mein Kampf, Vol. 1 Chapter 10

"This human world of ours would be inconceivable without the practical existence of a religious belief. The great masses of a nation are not composed of philosophers. For the masses of the people, especially faith is absolutely the only basis of a moral outlook on life. The various substitutes that have been offered have not shown any results that might warrant us in thinking that they might usefully replace the existing denominations. ...There may be a few hundreds of thousands of superior men who can live wisely and intelligently without depending on the general standards that prevail in everyday life, but the millions of others cannot do so."

- Adolf Hitler, Mein Kampf, Vol. 1 Chapter 10

"In short, the results of miscegenation are always the following: (a) The level of the superior race becomes lowered; (b) physical and mental degeneration sets in, thus leading slowly but steadily towards a progressive drying up of the vital sap. The act which brings about such a development is a sin against the will of the Eternal Creator. And as a sin this act will be avenged."

- Adolf Hitler, Mein Kampf, Vol. 1 Chapter 11

"Anyone who dares to lay hands on the highest image of the Lord commits sacrilege against the benevolent creator of this miracle and contributes to the expulsion from paradise."

- Adolf Hitler, Mein Kampf Vol. 2 Chapter 1

"Thus inwardly armed with confidence in God and the unshakable stupidity of the voting citizenry, the politicians can begin the fight for the 'remaking' of the Reich as they call it."

- Adolf Hitler, Mein Kampf Vol. 2 Chapter 1

"It doesn't dawn on this depraved bourgeois world that this is positively a sin against all reason; that it is criminal lunacy to keep on drilling a born half-ape until people think they have made a lawyer out of him, while millions of members of the highest culture-race must remain in entirely unworthy positions; that it is a sin against the will of the Eternal Creator if His most gifted beings by the hundreds and hundreds of thousands are allowed to degenerate in the present proletarian morass, while Hottentots and Zulu Kaffirs are trained for intellectual professions."

- Adolf Hitler, Mein Kampf Vol. 2 Chapter 2

"That this is possible may not be denied in a world where hundreds and hundreds of thousands of people voluntarily submit to celibacy, obligated and bound by nothing except the injunction of the Church. Should the same renunciation not be possible if this injunction is replaced by the admonition finally to put an end to the constant and continuous original sin of racial poisoning, and to give the Almighty Creator beings such as He Himself created?"

- Adolf Hitler, Mein Kampf Vol. 2 Chapter 2

"The folkish-minded man, in particular, has the sacred duty, each in his own denomination, of making people stop just talking superficially of God's will, and actually fulfill God's will, and not let God's word be desecrated. For God's will gave men their form, their essence and their abilities. Anyone who destroys His work is declaring war on the Lord's creation, the divine will."

- Adolf Hitler, Mein Kampf Vol. 2 Chapter 10

"To do justice to God and our own conscience, we have turned once more to the German Volk."

- Adolf Hitler in speech about the need for moral regeneration of German, February 10, 1933

"The fact that the Vatican is concluding a treaty with the new Germany means the acknowledgment of the National Socialist state by the Catholic Church. This treaty shows the whole world clearly and unequivocally that the assertion that National Socialism is hostile to religion is a lie."

- Adolf Hitler, speech to members of the Nazi Party on the Nazi-Vatican Concordant, July 22, 1933

"May divine providence bless us with enough courage and enough determination to perceive within ourselves this holy German space."

- Adolf Hitler in speech, March 24, 1933

"We don't ask the Almighty, 'Lord, make us free!" We want to be active, to work, to work together, so that when the hour comes that we appear before the Lord we can say to him: 'Lord, you see that we have changed.' The German people is no longer a people of dishonor and shame, of self-destructiveness and cowardice. No, Lord, the German people is once more strong in spirit, strong in determination, strong in the willingness to bear every sacrifice. Lord, now bless our battle and our freedom, and therefore our German people and fatherland."

- Adolf Hitler, Prayer, May 1, 1933

"I believe today that I am acting in the sense of the Almighty Creator. By warding off the Jews I am fighting for the Lord's work."

- Adolf Hitler, Speech, Reichstag, 1936

Source for the quotes: http://atheism.about.com/od/adolfhitlernazigermany/tp/AdolfHitlerReligiousFaith.htm

More on the issue of Nazis and Christianity: http://atheism.about.com/od/adolfhitlernazigermany/a/NaziChristian.htm?nl=1

(This piece was completely reworked on 3rd of October, 2012)