The following has been re-classified from Security Clearance Level 1 to Security Clearance Level 2 as of 01/10/19.

Addendum 258.1: When seven flatcars were attached to RPC-258, seven audible blips were heard followed by the standard ringing of a telephone. The tone of each blip corresponded to known numerical values on standard telephones; e.g. a flatcar that has 3 freight containers upon it represented dialing a "3". This confirmed theories that each individual flatcar acted as a numerical placeholder in a local phone number.

The first "numbers" that were input into the anomalous mechanism of RPC-258 resulted in telephonic reception on the other line, with individuals commonly answering in the typical, cordial fashion. A pattern emerged with each call, the events of which are summarized below:

• Individual answers the phone.
• Individual hangs up or repeats their greeting as if not hearing anyone/thing on the other end.⁴
• Individuals who remain on the phone can become increasingly panicked, particularly in their inquiries to what is occurring on the dialing end of the line.
• Loud and abrasive interference occurs and connectivity is lost.

Follow-up surveys revealed additional information:

• RPC-258 can only make calls to land lines.
• A call can be terminated at any time by releasing the horn.
• Calls outside the local area code can be achieved using three additional initial flatcars in tow.
• The same numbers that enacted the above pattern could be dialed again, but never resulted in an individual picking up the line. A busy tone sounded instead.
• The interference does not occur if an answering machine is engaged.

Addendum 258.2: Administration and Research coordinated more controlled testing designs, refurbishing a disbarred Authority landline-based comm network, MAGCOMM. Phones were placed at a variety of abandoned Authority stations and were equipped with modern-day advanced recording paratransmitters⁵ which provided detailed and real-time analysis of the received audio via Authority telecommunications equipment. The following are summary points of the reports, submitted since ██/██/19:

• There are no traceable features, including any physical coordinates to the instigating end of the communication.⁶
• When picked up, the receiver emits a faint dial tone that becomes increasingly louder at a rate of ~5dB per second over the course of 18.4 seconds. At a maximum decibel level (92dB), an explosion occurs, the payload of which is localized to any object that is affixed to the phone's receiver. The lethality of this blast for organic objects is inevitable.
• The damage observed is consistent with high-velocity impact forces and/or radial blast wave injuries. Neither the immediate environment nor the phone itself are affected by the force. The blast will not occur if the comm is disengaged prior to 18.4 seconds.
• If left off the hook in perpetuity, the explosion will re-occur at approximately the same time the phone was taken off the receiver each day thereafter, given that an object is affixed. Otherwise, the noise simply crecendos and decrecendos without event.
• Analysis of the swells indicates that after a blast occurs or would otherwise occur, the dial tone decreases in volume and frequency according to the principles of the Doppler effect.

Further testing has confirmed the following theoretical data:

• Explosion forces delivered to the recipient approach 1.9x 10⁷ N.
• The theoretical velocity of an object exhibiting the average periodicity of the observed Doppler shift would be ~80km per hour, near the maximum of known locomotives.
• The explosion forces measured suggest a theoretical mass of ~1.6x10⁷ kg.

Addendum 258.3: The above data correlates with the tonnage of the configuration of RPC-258 at the time of testing. Further calculations were consistent with modifications in load weights.

RPC-258's capabilities were confirmed to be reliably physical. Personnel in police forces and investigatory units near these numbers had been preemptively contacted in all testing; salvage operations involving in-network coroners and mortuaries are underway.

While RPC-258 cannot be traced to a location, tapping equipment regularly provides a local phone number: ██-██-██95, which is not officially registered. This number is unreachable via telephonic communication devices, including landline phones. However, if the number is input to devices with video calling capabilities, the call is answered — indicated per on-screen icons controlled by firmware — despite the video devices using the same communications technology as cell phones (tower and/or satellite). When dialed in this manner, RPC-258's horn will sound without manual engagement for the duration of the "connection" and as theorized will automatically [DATA EXPUNGED].

Video and audio feeds fail to capture any signals, displaying only a black screen and silence. To date, no actionable data has been obtained from these calls. Of note, the video feed self-terminates after approximately 18 seconds.

Incident 258.4: On 02/07/19 at ████ local time, RPC-258's horn sounded despite any known attempt at connection. The last phone number that had been dialed using RPC-258's means of connectivity, several months prior, was an abandoned Authority training facility involved in the MAGCOMM reboot. Sounds emanating from RPC-258 ended spontaneously at ████ local time, the call lasting [DATA REDACTED].

After the event, Authority field operatives discovered that this site had been obliterated in its entirety by a large explosive force. Using evidence from the wreckage, forensics confirmed that the site had been commandeered sometime after the reboot, and had been repurposed by a recent splinter cell of dissidents from within the Authority who were vying for power. Of note, technologically inclined members of the cell had apparently modified the landline to receive data that could be deciphered into video feed, for purposes of covert communications. This cell has since been neutralized completely.

Addendum 258.4: Repeated weights of RPC-258 (no attachments) showed discrepancies from initial measures. The extra weight was eventually discovered, localized to the locomotive’s engine intake cannula, which was found overflowing with [DATA REDACTED], including those of [DATA REDACTED], as confirmed by Authority HR records.