On 7 March 1939, after brief stints as Minister of Health and Minister of Education, he replaced Cristea as Premier upon his death, being considered the "man of steel" able to prevent the Iron Guard's political rise and to keep Romania out of the pro-German war camp (the nickname "The Man of Steel" probably originated, under the form "l'homme d'acier", in essays written by the French journalists Jérôme and Jean Tharaud on Romanian topics). However, he had been Prime Minister in all but name since February, when he was granted extensive powers in the wake of Cristea's illness. Călinescu was also Minister of the Interior and Minister of Defense. In September of that year, after the invasion of Poland, certain members of Iron Guard alleged that Călinescu and the King Carol planned with the British Intelligence services to blow up the Prahova oil fields, preventing Germany from taking control and using them.