Forbidden Zone Geocaches
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  Silverback Cipher  
Silverback hunters should be familiar with the “pigpen” or masonic cipher, which is a simple substitution cipher exchanging letters for symbols based on a grid.

This cipher can be used to decrypt directions and secret codewords at FBZ geocaches!

  External Links  
  · 1: The FBI Vault
· 2: The CIA Vault
· 3: Project Blue Book
· 4: Aliens the Truth

Supernatural Supernova
FBZ A.P.E. 55(a) - GC9PAQ3


SUBJECT: FBZ A.P.E. 55(a) Brief [Mission #5A]

TO: Silverback Operatives

The derelict structure located near the entrance to the Mount Soledad Veterans Memorial is a former World War II Army Command Post. Nicknamed the Old Blockhouse, it is one of many cement-fortified bunkers built on the surrounding hillsides after the Japanese attack on Pearl Harbor in 1941. S.G.T.F. believes this fortress contains secrets relevant to our extraterrestrial-primate investigations. It is feasible this buildings derelict condition is only a ruse; that government black ops are still regularly conducted here in the underground rooms now retro-fitted with highly sophisticated space and satellite equipment. Consequently, it should come as no surprise SGTF considers this sector to be highly relevant to our inquiries surrounding alien-primate phenomenon, UFO studies and paranormal activity.

Here you will discover the fifth (5th) in a series of codewords needed to unlock the final mission details for Operation Silverback.

Remember to use SGTF’s cipher at to decode secret writings discovered during this and other FBZ adventures.

In all, there are seven (7) FBZ locations (i.e. missions) to Operation Silverback. Six FBZs contain “intelligence” report(s) and a corresponding secret codeword. Enter the six (6) codewords collectively at to discover the seventh and final FBZ location. Keep in mind codewords can be gathered in any order so you DO NOT need to visit FBZs sequentially!

The seventh and final FBZ TSG location is where the “truth” related to Operation Silverback shall be revealed.


Operatives who have successfully submitted the TOP SECRET codeword for this mission...

  • Honorable Discharge FLAGMAN
  •  (Thu 01 Jun 2023 @ 22:04:35 BST; 1685653475 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Honorable Discharge THEJJDUO
  •  (Fri 15 Jul 2022 @ 13:27:42 BST; 1657888062 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • General DILLWEED
  •  (Thu 18 Aug 2022 @ 20:52:18 BST; 1660852338 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • Green Beret STANSD
  •  (Tue 05 Jul 2022 @ 16:16:15 BST; 1657034175 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • General OESTEADO
  •  (Sun 10 Jul 2022 @ 18:15:05 BST; 1657473305 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)
  • First Sergeant NOBRO58
  •  (Fri 31 Mar 2023 @ 19:07:43 BST; 1680286063 seconds since Unix Epoch (POSIX) 01 Jan 1970 00:00:00 UTC)

Mission 5 Report

FBZ A.P.E. 55(a) contains an ammo can with Special Reconnaissance (SR) related to SGTF's Operation Silverback in the form of Planet of the Apes Memorabilia (POTAM) and scouted intelligence reports. As a clandestine special tactics unit, SGTF has been known to leave POTAM tracking bugs in their FBZs with special mission instructions related to active Project A.P.E. caches (e.g. Project A.P.E. Mission 9: Tunnel of Light).

FBZs are reserved for POTAM related to SGTF's Silverback operations. Visitors are encouraged to register their visit and leave ONLY items containing relevance to The Planet of the Apes or items that are traditional hitchhikers (e.g. geocoins, travel bugs, etc.). Only place and/or remove TRACKABLE items from this cache (read NO unrelated SWAG); Any POTAM found in this cache designated as NOT TRACKABLE is pertinent to operations for this FBZ and should REMAIN ASSIGNED TO THE CACHE. POTAM labeled PROVISIONAL FTF is considered remittance as reward for the FTF (First to Find) and can be removed freely without restriction or stipulation.

Copyright © by Forbidden Zone Geocaches All Right Reserved.

Published on: 2009-01-19 (9376 reads)

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   Operation Silverback Prize Ring SILVERBACK Prize Rings

Those who create an account on and enter mission codewords and POTAM tracking bug numbers receive points towards an Operative ranking. Operatives who achieve the rank of General (700 points) are eligible to receive an official silver Operation Silverback trackable ring from Oakcoins. Gold rings are available for those who reach the rank of Green Beret (or higher).