what were the weapons used for the first time in world war 1?

Tanks

Armoured cars

Poison gas

Tear gas

Dreadnought battleships

Combat aircraft

Airships

Trench mortars

Aircraft carriers

Tracked large calibre siege mortars

Long range supergun artillery

Anti aircraft guns

Submarines, barbed wire, grenades and flamethrowers had all been used in battle some years before WW1, so are not included in my list.

As you can see, a lot of people think that the airplane was first used in WW I, but the Americans used them in the so-called "police action" against Mexican revolutionary, Pancho Villa.

A lot of people think that machine guns were first used here, too, though they had been used in various wars and skirmishes around the world, including the Spanish-American war. Ditto for armored cars.

Tanks, Airplanes, U-boats, Chlorine and Mustard Gas, Trenches

the armored tank, machine gun, chemical warfare in large menacing forms, submarines and torpedoes. wrist watches were introduced along with eastern standard time/ daylight savings time, mobile hospital units, blood transfusions, limited airplanes and aerial bombings, etc. the list is nearly endless on 'firsts'. WW1 is indeed the first modern war with items used that were never seen before.

Flamethrower, Gas bombs, Grenades, Airplanes, and Machine Guns

World War I was so deadly primarily because it saw the use of nineteenth-century military tactics with twentieth-century technology.

Before World War I, there were no machine guns. In addition, barbed wire, poison gas, and the automobile played big parts.

From Shmoop

the .303 rifle, the tank, a very early form of the aeroplane (as well as one that was designed to take off from the water), grenades and many more.

Bayonets, flamethrowers, grenades, machine guns, pistols, luger's, poison gas, rifles, tanks and trench mortars.

The flamethrower

The tank, airplane(bombers and fighters) and mustard gas