Japan's Prime Minister Fumio Kishida (left) rides on a Japan Ground Self-Defense Force (JGSDF) Type 10 tank during a review at JGSDF Camp Asaka in Tokyo on Nov. 27, 2021.

A collapse in the yen is forcing Japan to scale back a historic five-year, 43.5-trillion-yen defense build-up aimed at helping to deter a Chinese invasion of Taiwan, according to eight people familiar with the matter.

Since the plan was unveiled in December, the yen has lost 10% of its value against the dollar, forcing Tokyo to reduce its ambitious defense procurement plan, which was then-calculated to cost $320 billion, the sources said.