This trial is conducted in Europe. The aim of the trial is to investigate the Safety, Tolerability,Pharmacokinetics (the exposure of the trial drug in the body) and Pharmacodynamics (the effect of the investigated drug on the body) of subcutaneous NNC0143-0406 A 0.6 mmol/L in Subjects with Type 1 Diabetes

Inclusion Criteria:

• Male, aged 18-55 years (both inclusive) at the time of signing informed consent
• Subjects diagnosed (clinically) with type 1 diabetes mellitus at least 365 days prior to the day of screening
• Body mass index between 18.5 and 28.0 kg/m^2 (both inclusive)

Exclusion Criteria:

• Known or suspected hypersensitivity to trial product(s) or related products.
• Males who are sexually active and not surgically sterilised (vasectomy or otherwise) and their partners that are not using a highly effective contraception method, from randomisation until 90 days after dosing, such as double barrier contraception (e.g. condom and spermicide) or combination of either an oral contraceptive, a contraceptive patch, a diaphragm or intrauterine device, together with a physical barrier such as condom. Malesubjects must also agree to refrain from sperm donation from randomisation until 90 days after dosing
• History or presence of any clinically relevant respiratory, metabolic (including dyslipidaemia), renal, hepatic, gastrointestinal, endocrinological conditions (except conditions associated with diabetes mellitus)
• Subject who has donated any blood or plasma in the past month or more than 500 mL within 90 days prior to screening
• Smoker (defined as a subject who is smoking more than 5 cigarettes or the equivalent per day) who is not able or willing to refrain from smoking or use of nicotine gum or transdermal nicotine patches during the in-patient period
• Recurrent severe hypoglycaemia (more than 1 severe hypoglycaemic event during the past 180 days) or hypoglycaemic unawareness as judged by the investigator or hospitalisation for diabetic ketoacidosis within the last 180 days