The Safety Pen was the answer to the messy problem of leakage afforded by the Eye Dropper pens of the day. This advancement attempted to offer a solution to the problem of leakage by storing the nib inside the pen, thereby preventing the condensation of ink into the cap of the pen itself.  Waterman invented the Safety Pen in 1907 and replaced the usual push/slip cap with a screw cap (quite a deal at the time). Waterman continued to produce the Safety Pen beyond 1925, and some other companies (the innovation was widely copied) produced the pen well into the beginning years of WWII.

To fill the pen the user had to hold it upright and screw off the cap. At this point, the nib was still sunk into the barrel of the pen. The user then filled the pen in much the same fashion as they filled the old Eye Dropper, by using an eyedropper to fill the barrel to the top.  Keeping the opened end of the pen facing upwards to avoid spillage of ink everywhere, the cap was replaced on the lower end of the barrel and turned to secure it on. The end of the barrel was turned to the right which caused the nib to rise from the barrel of the pen and needed to be locked securely into place. The pen was ready to use once the ink was wiped from the end of the nib.