Were cavalry used in the First World War?

Cavalry was used only sporadically in World War I. On the Western Front, there were only a handful of divisions used for "special services" such as scouting and transport. http://en.wikipedia.org/wiki/British_cavalry_during_the_First_World_War

In the Eastern front, where distances were larger, cavalry was used as "spearheads," e.g. by the Germans at the battle of Tannenburg, and by Russia's General Brusilov.

Cavalry was also used in "peripheral" areas such as the invasion of Iraq (then held by the Ottoman Empire).

They were certainly used. But see John Terraine. He maintained it was irresponsible to plan an offensive without bringing up cavalry to exploit a success. Tanks from 1916 could break in, but not exploit. Cavalry couldn't fulfil their traditional role of exploitation, barbed wire and a machine gun stopped them.

They did not have what they needed - the Blitzkrieg tank. Warfare was at a hiatus in technology. World war 1 - also the only war fought without voice command.

At the risk of flogging a dead horse here, I think we need to mention another aspect - the attitudes of the top commanders. The most glaring example I have in mind is Haig who famously told young officers (the remark may be apocryphal but certainly reflective of his recorded opinions) in July 1914:

I hope none of you gentlemen is so foolish as to think that aeroplanes will be usefully employed for reconnaissance purposes in war. There is only one way for commanders to get information by reconnaissance, and that is by the cavalry

Well, that may be understandable, but amazingly the man persisted in this opinion and this is what he had to say in 1926 (yep, nineteen twenty-six, eight years after the end of the war):

I believe that the value of the horse and the opportunity for the horse in the future are likely to be as great as ever. Aeroplanes and tanks are only accessories to the men and the horse, and I feel sure that as time goes on you will find just as much use for the horse—the well-bred horse—as you have ever done in the past.

(quoted from a page that does a really admirable job of skewering Haig).

However, not all cavalry commanders of WWI were bloody cruel butchers like Haig. An example of a cavalry general who both did his job well (on the Eastern Front) and learnt enough in the process to realize that cavalry was over is Mannerheim.

One more thing worthy of mention: Celaya.

Yes. See Wikipedia.

All of the major combatants in World War I (1914–1918) began the conflict with cavalry forces. The Central Powers, Germany and Austria–Hungary, stopped using them on the Western Front soon after the war began. They continued to be deployed in a limited fashion on the Eastern Front well into the war. The Ottoman Empire used cavalry extensively during the war. On the Allied side, the United Kingdom used mounted infantry and cavalry charges throughout the war, but the United States used cavalry for only a short time. Although not particularly successful on the Western Front, Allied cavalry did have some success in the Middle Eastern theatre, possibly because they faced a weaker and less technologically advanced enemy. Russia used cavalry forces on the Eastern Front, but with limited success.

Although trench warfare is the image of WWI, not all the war was fought from or in trenches.

For example,

One of the last cavalry charges of the war came at the Battle of the Somme in 1916. The attack was on July 14th on High Wood – a German strongpoint that was holding up the British advance. Men from the 20th Deccan Horse, an Indian cavalry unit, attacked the German positions. Armed with lances and despite going uphill which slowed down the charging horses, some of the men reached the woods. Some Germans surrendered when confronted by cavalry in woodland – something they could not have expected. However, the attack, while brave, was very costly with 102 men killed along with 130 horses.

That is just from 10 minutes of cursory research; a more skilled scholar could doubtless pull up other examples.

Cavalry were certainly used during the First World War.

It is worth remembering that the First World War was a world war, and wasn't limited to the attritional trench warfare of the Western Front, which is often the first image that people call to mind when they think of that war.

To give just one example from another theatre of the war, the Battle of Beersheba, in Ottoman Syria on 31 October 1917, included what has often been called the "last successful cavalry charge in history". The 4th Brigade of the Australian Light Horse charged Turkish positions in the town (supported by British artillery which successfully suppressed Turkish machine-gun positions).

It seems appropriate to be answering this today, on the centenary of the charge of the Australian Light Horse, which was instrumental in the capture of the town of Beersheba.

The capture of Beersheba broke the Gaza-Beersheba defensive line, and the Ottoman Seventh and Eighth Armies were forced into retreat. Gaza would fall a week later, and on 9 December 1917, British troops entered Jerusalem.

Probably the only large cavalry charge is the one Australians performed during the battle of Beer Sheva. The ANZAC forces were in fact mounted infantry and the charge was performed with infantry weapons (no lances but rifles with bayonets), this was surprising for Turkish defenders. It was so quick that the Turks could not destroy wells.

On other fronts (especially in Poland, Russia and Romania) cavalry performed reconnaissance tasks, but played no major role in any battle. Many cavalry men changed forces; one of the most notable examples was Manfred von Richthofen, the best pilot during the war. He had the rank Rittmeister, which is cavalry captain. His brother, Lothar, also a famous ace, was a cavalry man too.

British Cavalry was surprising successful on the occasions it was employed by local commanders in small scale attacks exploiting gaps in the German defensive lines after the Germans had withdrawn to the Hindenburg Line from late 1916 onwards. Despite what many ill-informed commentators say, many citing quite erroneous accounts by eye-witnesses who get the fundamentals wrong because they did not see what happened but thought they knew what should have happened, death tolls were not always high. Charging horses, moving fast did manage to avoid much of the machine gun fire directed at them Additionally, British Cavalry Regiments contained a section of machine guns and horsed field artillery that could be employed to suppress German fire. High Wood is a good example although most of the casualties cited above were sustained well after the original charge and occupation of the High Wood hill. The true value of cavalry emerged as a means of exploiting a gap and pushing forward to occupy ground that the infantry were too tired to reach. It worked!

Many knowledgeable historians will also theorise that the 1918 German Offensive fails in part because strong cavalry forces were not available to German generals to push the British hard enough to completely break them. The absence of cavalry at brigade and divisional level meant that German infantry were advancing without being able to adequately protect the flanks of their attacks with cavalry.

Don't forget that all modern cavalry carried rifles and were trained to rapidly deploy them.