North Korea amps up electronic warfare

I don't like where this is heading:

A US military reconnaissance plane came under electronic attack from North Korea and had to make an emergency landing during a major military exercise in March, a political aide said Friday.
The aide said the plane suffered disturbance to its GPS system due to jamming signals from the North's southwestern cities of Haeju and Kaesong as it was taking part in the annual US-South Korea drill, Key Resolve.

[...]
Jamming signals -- sent at intervals of five to 10 minutes on the afternoon of March 4 -- forced the plane to make an emergency landing 45 minutes after it took off, the aide quoted the report as saying.
The signals also affected South Korean naval patrol boats and speedboats, as well as several civilian flights near Seoul's Gimpo area, according to the report.

Several major issues here.

First, while electronic warfare has been common for decades, I'm not aware of too many incidents where GPS has been jammed.  Obviously, it shows that our GPS systems, which are used by most of the world, are vulnerable. 

Second, this sounds like a small-scale test for effectiveness and reaction.  If we get into a military confrontation with North Korea, we can expect a lot more of this.

Which leads me to the third issue, which is more of a series of questions, which may be more of a series of criticisms: how can loss of GPS force down a plane?  Does it mean we can't navigate at all without GPS?  How the hell did we manage to win World War II, then? Last time I checked, those Hellcats, Dauntlesses, Mustangs and Flying Fortresses didn't have GPS; they had paper maps. 

Does this mean we can no longer navigate without GPS?

We are in trouble.

(Did you see what I did with the post title? Amps? Get it? Amps? Thangyouveramuch. I'll be here all week.  Remember to tip your waiters and waitresses.)