On the other hand, when Secret Service agents are working abroad they must perforce rely upon codes of sorts, for means of intercommunication between themselves, their friends and supporters. These codes are invented by them entirely at their discretion. If they are wise in their generation they never keep the same code too long in use, but change it, at frequent intervals, for another entirely different in every respect. Such codes cannot be too carefully prepared; whilst every user knows that if his deception is discovered the consequences to himself might be serious indeed. Simplicity is invariably the safest and most effective rule to follow. In order to give the reader a good idea of how the work was accomplished a couple of these codes are roughly outlined, with examples of their working in each case. One was used for sea work. It was a grammatical code, which, although simple enough in its patent aspect, was not easy to memorise with that strict accuracy which is so essential to future use. Shortly, this code ran somewhat on the following lines, although English names are therein substituted in order to give better illustration. Needless to add, these messages were worded in the language of the country in which they were despatched, and signed with an assumed name which would be in common use in that country. EXAMPLE 1. I. Communications signed with _Christian Name_ refer to _War Ships_. Communications signed with _Surname_ refer to _Merchant Ships_. II. _Please send a copy of_ "_The Times_" _to_ ... means "a base is being formed at ..." III. I received a letter from ... _on_ ... means {German auxiliary cruiser(s) in port at ... {German battleship(s) hanging about near ... IV. I received a message from ... _on_ ... means {German large merchant ship in port at ... {German cruiser hanging about near ... V. I am hoping to hear from ... _on_ ... means {German small merchant ship in port at ... {German torpedo-boat(s) hanging about near ... VI. I am expecting a message from ... _on_ ... means {German collier(s) in port at ... {German submarine(s) hanging about near ... VII. The _first blank_ in the sentence is to be filled in with the _name of the place_ at which the base is being formed, or at which the ships have been seen. VIII. The _second blank_ in the sentence, after the word "on" is to be filled in with a _day of the week_ indicating the number of ships seen (_see_ over, IX). IX. 1 is Monday 2 is Tuesday 3 is Wednesday 4 is Thursday 5 is Friday 6 is Saturday 7 is Sunday 8 is Monday-week 9 is Tuesday-week, and so on. 15 is Monday-fortnight, and so on.