This is John Bachelor, speaking with my colleague Colonel Jeff McCawson,

and nutted state's army retired, CBS News.

We address the matter of the tunnels in Gaza City.

How does the IDF approach the tunnels?

Unlike anything else in urban warfare, the tunnels operate

underneath your feet, and the enemy can pop up anywhere,

and Jeff tells one story about how to anticipate where the enemy may come out.

Colored smoke grenades down into the tunnel.

Jeff tells the story very carefully.

Still, the challenge is enormous.

The IDF is taking casualties.

Right now, the report from Jerusalem is 16 KIA IDF,

untold gone on the Gaza Hamas side.

They are in the tunnels, and in the underground passageways of Gaza City.

Here's Jeff.

Absolutely correct, John, or you've got to figure out some way,

perhaps by using riot agents or otherwise,

to force them to come out of the tunnels.

One thing I know the Israelis have used in past is, frankly,

colored smoke grenades that throw down into tunnel complexes,

and then stand back and see if smoke arises somewhere else down the street,

telling you where the exit point that particular part of the tunnels might be.

...