A red line-what is it, has it been crossed and whatmight that mean as far as the U.S. government isconcerned.

The red line we are talking about today involvesSyria.

A red line for us is we start seeing a whole bunch of chemical weapons moving around or beingutilized.

President Obama said that last August.

A recent attack that reportedly killed more than 1300 people is suspected of having crossed thepresident's red line.

Many governments and organizations consider chemical weapons worse than conventionalweapons like bombs or guns.

The United Nations describes chemical weapons as a crime against humanity.

Although some analysts say the impact of conventional weapons are just as awful for victims.

The idea of a red line is that once it'sbeen crossed, the person or country that's set it could take action.

Chris Lawrence examines what steps the U.S. could take next.

Within days, President Obama's national security team will present him with its final detailedoptions, and the administration is already making the case for taking action against Syria.

President Obama believes there must be accountability for those who would use the world'smost heinous weapons against the world's most vulnerable people.

Secretary of State John Kerry accused the Assad regime of gassing its own people.

IF the president gives the order, a senior defense official says, four Navy destroyers in theMediterranean Sea could execute a mission within hours.

U.S. and British submarines are also likely nearby, all armed with cruise missiles.

The extremely accurate Tomahawks can be fired from 500 miles away, with an ability tochange course in midflight.

The potential targets include the delivery systems that can be used to launch weapons.

Militia training camps being run by Bashar al-Assad.

And most importantly, the Syrian government's command and control centers.

Allahu akbar!

The options are not designed to overthrow Assad's government, but send a message anddeter any further use of chemical weapons, President Obama's red line.

In any time you throw down a diplomatic gauntlet, you words have repercussions.

The president is under some pressure to back up his own ultimatum.

And while the U.S. is consulting with allies, officials say, it may not need a formal coalition toexecute the response.

Chris Lawrence, CNN, the Pentagon.