B-25 aircraft in Them!
The B-25 aircraft that Dr Medford ( Edmund Gwenn )and his daughter arrive in about 17 minutes into the film was Paul Mantz's converted B-25 N1203 (you can see the tail number momentarily in the film) which he purchased as war surplus after WW II and converted into a flying camera platform for film work. You can see the rather odd nose on the plane as it taxis up to the gate and the awaiting characters played by James Arness and James Whitmore. Mantz used this plane to film the early aerial desert shots of the lost little girl in the film and the producer then used it for the shot of the B-25 taxiing to the gate. This is a rather famous plane. It had a glass panoramic nose fitted by Mantz (painted over for the film to resemble an Air Force aircraft) and several aerial sequences for Cinerama films were photographed from this aircraft (This is Cinerama, How the West Was Won, and It's a Mad Mad Mad Mad World..... in which Mantz flew a Beech 18 thru a billboard). This B-25H was also used extensively in the filming of Around the World in 80 Days (Todd-AO cameras)in 1956 and Catch-22 in Mexico in 1969. Mantz, a legendary aerial stunt flyer and CEO of Tallmantz Aviation (and friend of Amelia Earhart), was killed in July 1965 while trying to fly the experimental P-1 during filming of "The Flight of the Phoenix" near Yuma Arizona. (The actual film footage of the crash is up at youtube). The factoid they have in the trivia section here about the plane being the personal transport of a 2 Star General is incorrect. Here is a link for further information on this historic aircraft :
http://www.aerovintage.com/N1203.htm
What Mantz's B- 25 camera plane really looked like :
http://www.aerovintage.com/34643-3a.jpg
and how it appeared in Them! :
http://www.aerovintage.com/34643-2.jpg