When I slide the the write-protect switch to the locked position while the SS3 is connected to the computer, I am still able to write/delete data on the drive.
The SS3's write-protection switch must be set in either the locked or unlocked position BEFORE connecting it to your computer. Once the device is connected to a computer, it will remain in whichever state it is set in regardless of whether you change the switch position. In order to change the device's state from read/write to read-only or vice versa, you would need to safely remove the SS3 from the computer, set the write-protect switch to the desired position, and then reconnect it to the computer.
So, for example, if the write-protect switch was set in the unlocked position when the SS3 was connected to your computer the drive will operate in read/write mode for as long as it remains connected. In order to enable write-protection, you would need to safely remove the SS3 from the computer, set the write-protect switch to the locked position and then plug the drive back in the computer. The SS3 drive will now operate in read-only mode.