A Research Study of How Different Amounts of a New Medicine NNC0148-0287 C (Insulin 287) Works on the Blood Sugar of People Who Are Japanese With Type 1 Diabetes When Given Once a Week

This study will look at how insulin 287 works, if it is safe and the side effects in people who are Japanese with type 1 diabetes. The study will test how insulin goes through your blood, how long it stays there and how the blood sugar is lowered. Insulin 287 is a new medicine. Insulin glargine is already approved to treat diabetes. The study doctors can prescribe insulin glargine. The participants will get both of the insulins in a random order. The participants will get 8 weekly doses of insulin 287 and 14 daily doses of insulin glargine. There will also be a run-in period of 2 days to 7 weeks when the participants inject insulin glargine every day before they start insulin 287 period or insulin glargine period. All doses will be injected under the skin. During the run-in period, the participants adjust the insulin glargine dose and make their blood sugar levels stable. From the run-in period, the participants will take insulin aspart as bolus insulin. The study will last for about 16 - 28 weeks. The participants will have 24 visits with the study doctor. There will be 3 glucose clamps where the participants' blood sugar is tested over time. The participants cannot be in the study if the study doctor thinks that there are risks for their health.