Tom Swift Jr books by Victor Appleton II narrate the exploits of the son of Tom Swift.
Grosset & Dunlap first published the series in 1954 and ended the series in 1971. A total of 33 titles were printed.
The books were printed in 3 variations.
# 1-17 were originally published with dust jackets. In the early 1960's, these 17 books were reprinted as blue spine picture cover books.
#18 has a neat wrap around picture cover printing.
Later volumes, #19-33 were printed with orange spine picture covers.

Books in the Tom Swift Jr Series are:

#1 TOM SWIFT JR AND HIS FLYING LAB
#2 TOM SWIFT JR AND HIS JETMARINE
#3 TOM SWIFT JR AND HIS ROCKET SHIP
#4 TOM SWIFT JR AND HIS GIANT ROBOT
#5 TOM SWIFT JR AND HIS ATOMIC EARTH BLASTER
#6 TOM SWIFT JR AND HIS OUTPOST IN SPACE
#7 TOM SWIFT JR AND HIS DIVING SEACOPTER
#8 TOM SWIFT JR IN THE CAVES OF NUCLEAR FIRE
#9 TOM SWIFT JR ON THE PHANTOM SATELLITE
#10 TOM SWIFT JR AND HIS ULTRASONIC CYCLOPLANE
#11 TOM SWIFT JR AND HIS DEEP-SEA HYDRODOME
#12 TOM SWIFT JR AND THE RACE TO THE MOON
#13 TOM SWIFT JR AND HIS SPACE SOLARTRON
#14 TOM SWIFT JR AND HIS ELECTRONIC RETROSCOPE
#15 TOM SWIFT JR AND HIS SPECTROMARINE SELECTOR
#16 TOM SWIFT JR AND THE COSMIC ASTRONAUTS
#17 TOM SWIFT JR AND THE VISITOR FROM PLANET X
#18 TOM SWIFT JR AND THE ELECTRONIC HYDROLUNG
#19 TOM SWIFT JR AND HIS TRIPHIBIAN ATOMICAR
#20 TOM SWIFT JR AND HIS MEGASCOPE SPACE PROBER
#21 TOM SWIFT JR ANDTHE ASTEROID PIRATES
#22 TOM SWIFT JR AND HIS REPELATRON SKYWAY
#23 TOM SWIFT JR AND HIS AQUATOMIC TRACKER
#24 TOM SWIFT JR AND HIS 3-D TELEJECTOR
#25 TOM SWIFT JR AND HIS POLAR-RAY DYNASPHERE
#26 TOM SWIFT JR AND HIS SONIC BOOM TRAP
#27 TOM SWIFT JR AND HIS SUBOCEAN GEOTRON
#28 TOM SWIFT JR ANDTHE MYSTERY COMET
#29 TOM SWIFT JR AND THE CAPTIVE PLANETOID
#30 TOM SWIFT JR AND HIS G-FORCE INVERTER
#31 TOM SWIFT JR AND HIS DYNA-4 CAPSULE
#32 TOM SWIFT JR AND HIS COSMOTRON EXPRESS
#33 TOM SWIFT JR ANDTHE GALAXY GHOSTS

I have many Tom Swift Jr Books in my eBay Store.  If you don't see the title you want, bookmark my store and visit again, we are always acquiring more books!