According to the literature, 8% of the population claim to have an allergy to penicillin. Allergy tests show that 90% of these patients tolerate this molecule. Physicians working in the French Navy are faced with situations of real isolation and only have a limited number of antibiotics on board, the majority of which are penicillins. They must anticipate the risks linked to the prescription of antibiotics prior to the mission. However, there is no French recommendation, either military or civilian, intended for general practitioners clarifying the management and allergy assessments of patients alleging a history of allergy to penicillin. This study is the first to evaluate the professional practices of French military practitioners taking care of these patients. The main objective was to evaluate the proportion of sailors who reported an allergy to penicillin and who have never been referred for a consultation with an allergist, by studying the medical files of all the submariners working on the submersible ballistic nuclear submarines (SSBN) squadron in Brest. The secondary objective was to compare these data with the practices of Navy doctors by means of questionnaires. Material and methods : Exhaustive monocentric study of the digital and paper medical files of Brest submariners (n=814) looking for allergist consultation reports in cases alleging an allergy to penicillin, then comparaison with a multicentric collection of all Navy doctors' practices collected by an anonymised questionnaire (n=37 out of 53 practising at the time of the study). Results : Forty-seven subjects out of 814 alleged an allergy to penicillin (5.8%). Among them, only 12 (25.5%) had undergone allergy tests, of which 3 (6.4%) were confirmed to be allergic, with no cross- reaction between B-Lactam antibiotics. Yet, according to the questionnaire, 25 doctors (67%) report referring their patients to an allergist and 16 (43%) report having had difficulties at sea in connection with the prescription of antibiotics for these patients. Conclusions: A study of medical records shows that the allergic risk is not anticipated for 74.5% of patients labelled allergic, despite the difficulties encountered at sea. Standardisation of practices within the French Navy is necessary to avoid the prescription of second-line antibiotics, less effective and sometimes unavailable on board, and to improve patient safety in isolation situations. In agreement with French military allergists, we propose, in this article, guidelines for a systematic exploration of allegations of allergy to Penicillin in the French Navy.