The Post Office Investigators invented rather interesting gadgets to prevent crime.

The Post Office Investigation Branch is the oldest recognised criminal investigations force in the world. For more than 335 years it has worked to detect offences against the post and prosecute the perpetrators of these crimes.

A wave of big money robberies targeting banks and Post Offices in the 1950s and 1960s led to the invention of a variety of crime prevention gadgets. Here are our top five weird and wonderful devices.

1. Security Case

Security Case, late 20th century (2002-0188)

When activated, two extendible arms spring 1.5 metres from either side of this security case, making it difficult for a robber to escape with the valuables contained. See how it all worked, plus some more clever inventions, in the video below.

Now for the tech geeks. Take a look at the inside structure of the case thanks to these detailed manuals, in strictest confidence obvs!

Security Case Manual 1

Security Case Manual 2

Security Case Manual 3

2. Reinforced Hat

Reinforced Hat, c.1950 (E6065/1)

This might look like a typical tweed hat but it has a secret. It’s reinforced to protect the wearer during potential attacks.

3. Thief Catching Device

A thief catching device in action

This weapon-like device is activated by a hair spring trigger which shoots out an entangling nylon ‘anti-getaway net’ to catch a thief.

4. Protective Vest

Protective Vest, 1994 (2012-0043/7)

Protective body armour is used by postal staff when carrying out ‘Cash in Transit’ duties.

5. Invisible Ink

Marking kit, c.1990 (2012-0043/22)

If greeting cards consistently disappear on a postal route, test envelopes with secret identifying codes written in invisible ink were planted. Later, a second solution would be painted on, revealing the code when a suspect was challenged. Easier to use UV ink replaced this two-solution invisible ink.

UV Marking Kit, c.2001 (2012-0044/3)

This ultra-violet marking kit was used by the investigators to covertly mark postal packets and letters.

Find out more about the work of The Post Office Investigation Branch here.

– The Postal Museum’s Collections Team