The Imperial Japanese Navy (IJN) has indeed developed a reputation as the "cautious" service, cognizant of the danger of war with the United States and determined to avoid it, in contrast to an aggressive army eager for war at every turn. While the IJN was more opposed to the outbreak of war than the Army, the Navy was not necessarily more sensible or less-warlike than their Army counterparts.

To use a single example, in the lead up to the outbreak of the wider Pacific War, the Army was the primary driver for operations south against the European colonial holdings, commonly known as the "Southern Operation". The Army's original plan for operations south against the European holdings following the conclusion of the War in China quickly switched to seeing the Southern Operation as a way to bring the War in China to a conclusion. Primarily, the Army saw continued resistance by Chiang Kai-shek as being due to outside aid he and the Nationalist forces were receiving from outside. By going to war with the Europeans, the Japanese hoped to both occupy the resources of the European colonies as well as cutting off the Nationalists from outside aid, which would in turn enable the Japanese to finally bring the War in China to a close. The IJN in turn ended up in a delicate dance. From the Navy's perspective, the Southern Operation was far superior option to operations north against the Soviet Union, insofar as the continual budgetary war between the two services was concerned. Operations north would almost certainly sideline the Navy, putting the Navy's dreams for expansive naval construction on the bottom of the pile, while operations south promised a substantial role for the Navy. Indeed, the Army had inquired whether operations south could proceed without attacking the Philippines and thus bringing the United States into the war, but the Navy had insisted that operations against the European colonies would have to include the Philippines and thus the United States. The need to include the United States helped to justify the Navy's own push for a substantially larger share of national resources in the lead up to the war, enabling the Navy to push an extensive naval construction program.

At the same time, the Navy was very concerned about the prospect of war with the United States, as it seriously questioned whether it would be able to win a war with the United States. Instead, the IJN opted for trying to both have its cake and eat it too. By encouraging the Southern Operation, the IJN could continued to ensure it would receive a larger share of national resources that it could rightfully claimed were necessary for the successful prosecution of the operation. Yet, the IJN also attempted to slow down the tempo of the Southern Operation, hoping that it could avoid provoking a war with the West, much the Army's frustration. I go into more detail about the internal war over Japanese policy here. Ultimately, what forced an end to the situation was the sharp U.S. reaction to southern Indochina, including the freezing of Japanese assets and oil embargo, which convinced all Japanese leadership that the Southern Operation would have to be launched immediately, with great haste.

So, the answer to whether the IJN was the more "mature" or peaceful branch, almost certainly not. The IJN was as keen on war as the Army, and encouraged war against the US regardless. At the same time, the Navy sought to delay the start of the war, but more out of a desire to milk a politically advantageous situation as well as avoiding having to force a showdown it was uncertain about winning. Undoubtedly, a grand part of why the IJN has received such a favorable reputation is a question I can't answer, and that would involve much more looking at later history of popular memory, but the lionisation of Admiral Yamamoto Isoroku beyond all measure, and the resultant rub-off of that reputation likely has something to do with it.

I hope this has helped answer your question, and please feel free to ask any follow ups.

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