Science of war-airforce-lighter than air vehicles.

Science of Conflict Air force-lighter than air vehicles
The first air force was established in March 1794, the Compagnie d'Aeronautiers, the Balloon Corps. Balloons were used for reconnaissance during the Battle of Fleurus in June 1794 and gave the French notice of Austrian troop movements up to one hour before they were visible from ground level. Napoleon later took the Balloon Corps to Egypt in 1798 but they were never used as the British raided the camp and destroyed them before the Battle of Abourik. Napoleon later disbanded the Balloon Corps
Count Ferdinand Von Zeppelin, pictured on the right, served in the American Civil War as a foreign attache and witnessed first hand the use of balloon in war. He went on to design dirigibles and in 1905 secured a contract to supply the German military.
At the beginning of the First World War the German Army had an entire fleet of dirigibles or better known as Zeppelins. They were used in over five hundred raids over France and as far as London between 1914 and 1918. Zeppelins were largely ineffectual causing more anger than devastation. Such airships were slow and easy targets from ground attack. They were also constructed with hydrogen gas, a highly flammable substance that was to prove the demise of the airships after the Hindenberg disaster of 6 May 1937.
Why are most hot air balloon launched on a cold winter morning? How are modern airships kept afloat? What are the properties of helium that make it useful for the construction of airships?