Inside Japan's Iwakuni marine base is a slice of Americana. The canteen is adorned with solemn portraits of former presidents and tributes to fallen US troops. Televisions on the walls flicker with US sports programming as marines tuck into tacos and cheesecake. The sight of American and Japanese soldiers on the same base in Hiroshima can be a surprise. The site is just a few kilometres from where the Pacific war ended in a nuclear holocaust unleashed from a US bomber on August 6, 1945, that killed 140,000 people. The troops have shared the Iwakuni base for decades as part of a half-century alliance that shelters Japan beneath the world's largest military and nuclear umbrella. Behind these fences, the two sides salute each other, co-operate in military exercises and swap tactics. However, while US troops get to fire live weapons around the world, Japanese troops must stay at home, tied by constitutional restrictions - ironically written by the Americans during their postwar occupation of the country - that forbid military engagement. Those restrictions are a hindrance to the military ambitions of both sides. Iwakuni is the closest military airfield in Japan to the Korean demilitarised zone, and, as it has since the outbreak of the Korean war in 1950, the US wants all the help it can get. 'If anything happens, we will be in the hotspot,' said Master Sergeant Lesli Coakley of the base's public affairs office. Her Japanese colleague, Maritime Self-Defence Force (MSDF) Captain Shoji Satoru runs his stick across a map showing Korea, China and Taiwan. 'This is the area we have to watch out for,' he said. 'Strategically, this is the most important base in Northeast Asia.' With the help of the US, Japan has built a formidable war machine with an annual budget of US$41 billion. In addition to hosting more than 40,000 US soldiers on 89 bases such as Iwakuni, the world's second-largest economy boasts an army of 238,000, among the best-equipped on the planet. Just two weeks ago, Japan launched its own ballistic missile defence operation when it deployed its first ground-based Patriot Advanced Capability-3 interceptor system. The country's 45,000 air self-defence force personnel fly a fleet of about 200 F-15 fighters, one of a handful of militaries, including Saudi Arabia and Israel, allowed to buy them from the US. The country also has 32 F-2 fighters, 109 P-3C long-range aircraft, 16 conventional submarines and four Aegis-equipped destroyers, carrying a price tag of about US$1 billion each. This, in other words, is an army dressed up with nowhere to go. The incongruous 'defence' force military hardware on display in Iwakuni includes state-of-the-art electronic firing ranges, flight simulators and a US$500 million fleet of 10 Sikorsky helicopters dedicated to sweeping for mines, despite the fact that nobody has planted a mine in a Japanese harbour in decades and nor is anyone likely to. 'They're just in case something happens,' said a Japanese pilot. The half-century taboo on going to war has kept uniformed Japanese troops mostly out of the sight. 'Many Japanese people are unaware of the fact that their country has an army under another name,' wrote Richard Tanter, senior research associate at the Nautilus Institute for Security and Sustainability, who points out that, unlike America, uniformed troops are rarely seen in public in Japan. 'For substantial parts of the population, the armed forces of the country are not just unconstitutional, but deeply illegitimate,' he said. The Iwakuni soldiers - Japanese and US - change into civilian clothes when they step off base. The taboo has prevented Japan from building bombs, bullets and landmines, but it does make ships, submarines and large sections of the thousands of commercial airliners that fly around the world. And as a major nuclear power, all that is standing in the way of an A-bomb is a political decision that is gaining momentum, under Prime Minister Shinzo Abe, in the wake of mounting tensions with North Korea. Mr Abe has unambiguously declared his intention to scrap the war-renouncing Article 9 of the Constitution, written in 1947 under US occupation. This year, Japan's Defence Agency was formally upgraded to a ministry, 'the most important change in Japan's national security system since the agency and the Self-Defence Forces (SDF) were established in 1954', said the Asahi newspaper. The spectre of a remilitarised, aggressive Japanese nationalism is something of a journalistic cliche and is rejected by some, who call it a much needed readjustment to the new security realities of Asia. Some describe it as merely a great power sloughing off the outdated constitutional shackles of the cold war and say China, which is not above exaggerating the Japanese threat for its own political ends, is the real menace to the region. That ignores the tit-for-tat nature of rearmament. Japan's resolve to push a joint missile defence system, which was handed a recent budget increase of 30 per cent - to 182.6 billion yen (HK$15 billion) - provoked a warning from Beijing that it could 'destroy the balance of international security forces and ... cause a new arms race'. Moreover, the profound, post-1990 reordering of the country's political and military architecture is built on unsteady foundations. Tokyo is yet to convince the rest of Asia that it has come to terms with its past wartime aggression. As it moves closer to its American military partner and sheds the decades-old restrictions on military activity, the prospect of a remilitarised Japan worries many neighbouring countries. The country's uneasiness with history is on display at a museum in the nearby maritime base town of Kure, dedicated to the Yamato, the biggest battleship of the second world war. The museum is filled with passive expressions such as 'extension of the battle lines', as though the war, like bad weather, simply descended on the people of Japan, instead of being fuelled by political decisions. In the MSDF base in Edajima, young military officers graduate as they did 70 years ago under a shower of cherry blossom petals. An ancient cherry blossom tree in the courtyard is the subject of a famous wartime song, Doki No Sakura, sung by doomed kamikaze pilots, who are eulogised in an on-base museum. Inside Edajima and Iwakuni, the young soldiers on both sides have long ago ceased caring about what went on six decades ago. SDF troops walk past portraits of presidents their predecessors would have spat on, and US F/A-18 Hornet pilots wear insignias that mix the once-hated symbol of the Japanese Imperial Army - the rising sun - with stars and stripes. 'The war was a long time ago,' said Sgt Coakley. The troops are gearing up for a massive base expansion in which the number of US aircraft and personnel will double (to 6,000 people) and a US$2.5 billion offshore runway will be built, funded by the Japanese taxpayers. Japan already pays for about half the costs of hosting its US guests, or about 230 billion yen a year, according to Tanter. Outside, however, some are reluctant to let go of the past so easily. 'There are people who see joint military co-operation as a sign of progress, but not me,' said Ayako Nishimura, who campaigns for the closure of all US bases in Japan. 'We are going backward, not forward.' Mr Nishimura has been heartened by a local referendum last year in which 89 per cent of voters opposed the base expansion. But most military commanders around this city, rebuilt from the ruins of a war that happened long ago, say this is a temporary pothole on the road to a brave new future when American and Japanese troops will finally fight on the same side. 'I want to contribute to international society,' said Japanese chief petty officer Taguchi Osamu. 'That's why I joined the SDF.'