Balloon

A balloon was an inflatable bag filled with gas. It had a wide variety of purposes.

Transportation
In the 17th century, the Eleventh Doctor escaped from the Tower of London in a hot-air balloon, which witnesses called a "magical sphere". (TV: The Impossible Astronaut)

In 1851, Jackson Lake used a hot-air balloon called a TARDIS. (TV: The Next Doctor)

In 1863, the Third Doctor and Charlie Fisher used a hot-air balloon to help sketch a map of the Confederate lines. (COMIC: Backtime)

In 1890, Pierre Bruyére attempted to travel to the North Pole in a hot air balloon but was caught in a time loop, constantly taking different companions each time until he finally took Martha Jones and the Tenth Doctor who helped him to break the cycle of the creature that was feeding off him. (PROSE: The Frozen Wastes)

In India in 1926 the Fifth Doctor stole a hot air balloon in order to chase a steam train. (AUDIO: The Emerald Tiger)

In the 1940s, barrage balloons were used in the United Kingdom during World War II. (TV: The Empty Child)

In the 21st century, a picture of a hot-air balloon was on display in a space museum. (TV: The Seeds of Death)

On Spiridon, the Third Doctor improvised a hot-air balloon from plastic sheeting, enabling him and the Thals to escape the Daleks. This inspired him to take up hot-air ballooning as a hobby because he found it "most exhilarating." (TV: Planet of the Daleks)

When the Sixth Doctor took the TARDIS into Astrolabus' realm, it passed by a hot-air balloon. (COMIC: Once Upon a Time Lord)

Science
In the 1970s, Dr Tyler used balloons to carry devices which monitored cosmic rays. One of these accidentally picked up a gell guard. (TV: The Three Doctors)

While on Storm Mine 4, Chub carried out experiments with weather balloons. (TV: The Robots of Death)

The Eleventh Doctor used two toy balloons to illustrate the difference between the main universe and the pocket universe in which Hila Tacorien was trapped. (TV: Hide)

Toys
In 1913, Daughter of Mine carried Lucy Cartwright's red balloon with her after taking over her body. (TV: Human Nature)

In 1914, Aphasia carried a red balloon with her. (PROSE: Human Nature)

As a child, Alistair Gordon Lethbridge-Stewart lost a red balloon. The Eighth Doctor later changed time to a minor extent so that he caught the balloon and returned it. (PROSE: The Shadows of Avalon)

Balloons were often used by clowns, such as Odd Bob the Clown, (TV: The Day of the Clown) Clara the Clown, (TV: The Celestial Toymaker) and Chuckles and Boris. (TV: Robot Gladiators)

A young Mikhail lost his balloon. The Eighth Doctor found him a new one. (PROSE: Reversal of Fortune)