By Michael Drummond, foreign news reporter
The threat to shipping posed by GPS jamming and other interference is growing and there is a "real risk to life", experts have warned.
Hundreds of vessels are being affected every day, with disruption posing urgent risks to maritime safety.
The issue of interference to global navigation systems has rocketed in recent years, with disruption to aircraft perhaps more well-known than shipping.
Russia is accused of widespread jamming and spoofing operations in eastern Europe (Moscow has denied the accusations), but the problem has been observed all over the world.