diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..485dee6
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.idea
diff --git a/2021_01/submarine_depth.py b/2021_01/submarine_depth.py
new file mode 100644
index 0000000..390912c
--- /dev/null
+++ b/2021_01/submarine_depth.py
@@ -0,0 +1,42 @@
+from dataclasses import dataclass
+from typing import Optional
+
+MEASUREMENTS = (
+    199,
+    200,
+    208,
+    210,
+    200,
+    207,
+    240,
+    269,
+    260,
+    263,
+)
+
+
+@dataclass
+class Sonar:
+    last: Optional[int] = None
+
+    def calc_measurement(self, new_measurement: int):
+        if self.last is None:
+            direction = 'N/A no previous measurement'
+        else:
+            if self.last < new_measurement:
+                direction = 'increased'
+            else:
+                direction = 'decreased'
+
+        print(f'{new_measurement}: {direction}')
+        self.last = new_measurement
+
+
+def main():
+    sonar = Sonar()
+    for measurement in MEASUREMENTS:
+        sonar.calc_measurement(measurement)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/2021_01/submarine_depth_iter.py b/2021_01/submarine_depth_iter.py
new file mode 100644
index 0000000..3366db0
--- /dev/null
+++ b/2021_01/submarine_depth_iter.py
@@ -0,0 +1,37 @@
+MEASUREMENTS = (
+    199,
+    200,
+    208,
+    210,
+    200,
+    207,
+    240,
+    269,
+    260,
+    263,
+)
+
+
+def _calc_measurement(x: int, y: int):
+    if x - y > 0:
+        return f'{x}: increased'
+    return f'{x}: decreased'
+
+
+def main():
+    it_a = iter(MEASUREMENTS)
+    it_b = iter(MEASUREMENTS)
+    print(
+        f'{next(it_a)}: N/A - no previous measurement\n' +
+        '\n'.join(
+            map(
+                _calc_measurement,
+                it_a,
+                it_b
+            )
+        )
+    )
+
+
+if __name__ == '__main__':
+    main()