Chinese scientists want to use lasers to power ultrafast, stealthy submarines. A laser expert says there's a major flaw in their plan.

• The US and China are in a race to develop the most advanced submarines.  
• Chinese researchers say they have made a breakthrough in laser propulsion technology that could one day be used on submarines and missiles.
• A laser propulsion expert at McGill University told Business Insider they see flaws in the claims. 

Submarines have long been known as the silent hunters of the deep, lurking undetected under the surface.