It employs a table where one letter of the alphabet is omitted, and the letters are arranged in a 5x5 grid. Typically, the J is removed from the alphabet and an I takes its place in the text that is to be encoded. This time, it was Nils Kopal. It was championed by Lord Playfair (hence the name) and used by Britain in the Boer War and both World Wars and also by Australia and New Zealand in World War II.
This one was based on a ciphertext with only 40 letters. In order to check if if is possible to do better, I published another Playfair challenge.

An Efficient Modification to Playfair Cipher ... possible keys that are strong enough to withstand attacks and this makes it very difficult for the eavesdropper to get the information. For example, if ‘A’ is encrypted as ‘D’, for any number of occurrence in that plaintext, ‘A’ will always get encrypted to ‘D’.
It is said that it was rejected for use by the British Foreign Office due to its perceived complexity. Below is an unkeyed grid. Nils wrote: “We broke it with CrypTool 2 and George Lasry’s Playfair analysis algorithm (based on simulated annealing). History of the Playfair Cipher The Playfair cipher was created in 1854 by Charles Wheatstone. The Playfair cipher was the first cipher to encrypt pairs of letters in cryptologic history.

Again, one of my readers solved it. Source: Bonavoglia. [2] [3] Wheatstone invented the cipher for secrecy in telegraphy , but it carries the name of his friend Lord Playfair , first Baron Playfair of St. Andrews, who promoted its use.

Monoalphabetic cipher is a substitution cipher in which for a given key, the cipher alphabet for each plain alphabet is fixed throughout the encryption process. The Playfair cipher is a digraph substitution cipher. Totally different variety of cipher attacks has been thought of and non-vulnerability of recent cipher has been mentioned Also Srivastava et al.