Each is 5.25x7-5/8" hard cover with an average of 218 pages. Each has single b/w frontispiece illustration by E. Warren. Dates and titles are "1940 Don Winslow Of The Navy, 1940 Face To Face With The Scorpion, 1941 Breaks The Spy Net, 1941 Saves The Secret Formula". Dust jacket art includes Don on ship deck watching enemy plane go down in sea, men firing pistols at large plane with inset art of Don, Don gagging spy and listening to other spy torturing man in chair, and Don and friend being approached by sinister man in black clothes in desert. Dust jackets have bit of wear around edge with spine fade. Dust jacket for second title has 1.5" diagonal clip on inside flap with Christmas seal glued in place on text. Dust jackets overall VG/Fine. Books are overall clean, tight and Exc. Rare to find as a set with dust jackets.