Twenty Japanese offices and homes were raided late last month by more than 200 investigators on suspicion that Yamaha was attempting to unlawfully export its R-Max unmanned helicopters to China.

The aircraft in question are unmanned rotary-wing aircraft powered by a 246-cc, 21-hp engine, and were ostensibly designed for aerial application of agricultural chemicals. But, critics had charged, the helicopters’ payload could be converted for biological weapons use, or for military reconnaissance.

Yamaha acknowledged it had exported nine of the unmanned helicopters through a Chinese company–Beijing BVETechnology–since 2001 and said a 10th was being readied for export when the raid occurred. Japanese police also investigated records at the Tokyo offices of Beijing BVE, and said the business might be linked to the Chinese military.

Amid terrorist concerns last year, Japan strengthened its controls on the export of unmanned civil aircraft that carry more than 5.2 gallons of liquid.

Yamaha Motor director Toyoo Otsubo told reporters that the company was surprised by the allegations. He said Yamaha thought it had followed proper export procedures and added that the Japanese Trade Ministry gave no indication that the helicopters could not be sold to China.

Yamaha now faces charges of violating Japanese foreign trade control laws.