Japanese Constitution, despite recent attempts to change that, still contains Article 9, renouncing war:
ARTICLE 9. Aspiring sincerely to an international peace based on
justice and order, the Japanese people forever renounce war as a
sovereign right of the nation and the threat or use of force as means
of settling international disputes. (2) To accomplish the aim of the
preceding paragraph, land, sea, and air forces, as well as other war
potential, will never be maintained. The right of belligerency of the
state will not be recognized.
There have been two recent attempts to modify the constitution, including above mentioned article
2005 constitution draft:
First paragraph of Article 9, renouncing war, is retained. The second
paragraph, forbidding the maintenance of "land, sea, and air forces,
as well as other war potential" is replaced by an Article 9-2 which
permits a "defence force", under control of the Prime Minister, which
defends the nation and may participate in international activities.
This new section uses the term "軍" (gun, army or military), which has
been avoided under the current constitution. Also, addition in Article
76 of military courts. Members of the Japanese Self-Defense Forces are
currently tried as civilians by civilian courts.
2012 draft (emphasis mine):
National Security: The LDP draft deletes the current provision declaring that armed forces and other war potential shall never be
maintained, and adds new Articles 9-2 and 9-3 stating that the
"National Defense Force" shall be set up and the Prime Minister shall
be its commander-in-chief. According to the papagraph (3) of the new
Article 9-2, the National Defense Force not only can defend the
territory from a foreign attack and can participate in international
peacekeeping operations, but also can operate in order to either
maintain domestic public order or to protect individual rights.
Note, that this is only a draft and there is long way from this draft to actually changing the constitution:
Draft changes can be submitted to the Lower House with the support of
100 or more lawmakers, while Upper House lawmakers need the support of
at least 50 members. The proposals must be made item by item in
accordance to each individual theme and not as a whole package.
Article 96 stipulates that the draft must ultimately be approved with
a two-thirds vote in both chambers before being put to a public
According to the 2010 referendum law, all Japanese citizens aged 18
and older can participate in the referendum and the bid must win a
majority in order to actually take effect.
Experts said there are many hurdles in the technical process, making
it difficult to amend the Constitution — a fact that is criticized by
those in favor of change and welcomed by opponents. (source)
Japan is anything but weak militarily:
Despite calling its troops the "Self-Defense Forces," Japan has one of
the world's biggest military budgets at 4.81 trillion yen (41.6
billion dollars) a year. (source)
The Japanese navy is one of the most powerful in the world, with numerous very modern and powerful ships such as for example 6 AEGIS destroyers (source) (4 Kongō class and 2 Atago class). In fact their navy ranks 4th, behind USA, Russia and China, but ahead of UK, France and India (source).
Apart of aforementioned draft changes to the constitution, there have been some changes to Japanese military structure. For example in 2006 Ministry of Defense was created, before there have been only Defense Agency with much lower status, than fully-fledged ministry (source). One of the consequences of that is that overseas deployments no longer need approval of the parliament (source as above). Another consequence of that was changing prefix of JMSDF's ships from JDS (Japanese Defense Ship) to JS (Japanese Ship). Seems like a minor name change, but shows direction of the changes.