This is an Esterbrook CA cartridge fountain pen in blue c. 1961. The model number was CA101, and the identical pen with an aerometric filler was the A101. It is an all plastic cartridge pen that was promoted as the “only pen that lets you do this: carry two big cartridges” as it can hold two cartridges in the barrel. It also continued the use of the 32 different available Esterbrook Renew Point replaceable stainless steel nib units. The 5 1/4 inch long pen came in six colors: navy blue, blue, green, orange, gray and white and sold for $1.95.